Abstract 
Aimed at the hotspot in vegetation construction and eco-environment sustainable development and requirement of the assessment of ecosystem health in the Loess Plateau, taking on the eroded soil in long trial sites located in Ansai Reaseaech Station of Soil and Conservation research object, through the approach of substituting the temporal serial with spatial serial, the dynamics of  soil microbial characteristics, biochemical activities and active organic carbon pool were studied systematically and their implications for ecological rehabilitation were analyzed in this dissertation. The goal was to provide scientific reference and enrich the theory for vegetation rehabilitation and assessment of soil quality as well as biological effect in the hilly Loess Plateau. The main results are as follows: 
1. Soil physico-chemical properties and anti-erodibility of different vegetation restoration models was compared. The results showed that soil anti-erodibility and physical and chemical properties increased apparently in different modes of abandoned arable land, closing hillsides, artificial woodland and grassland, construction terrace and so on, and increased slowly with the extension of rehabilitation process. Different types of vegetation restoration are different in improving soil properties. In general, mixed woodland had the most remarkable effect, followed by fallow land and pure woodland was the smallest. It need a long time to reach to the soil quality of middling level, altitude level and the climax before vegetation destruction and the time is different in eco-environment restoration models.
2. Soil microbial biomass and SIR were low and can increased apparently through vegetation rehabilitation in the hilly Loess Plateau. The time to reach to the climax before vegetation destruction is a long time, maybe more than 100 years. The dynamics of soil microbial respiration was complex in different vegetation restoration models. The first kind is abandoned arable land which soil microbial respiration was enhanced rapidly in the initial stages of abandoned then kept a relatively stable state. The second is closing hillsides on northern slope and artificial woodland which soil microbial respiration was enhanced in the early stage and then weakened in the late stage. The third kind is orchard, terrace and closing hillsides on southern slope which soil microbial respiration was enhanced with the utilization period. Metabolic quotient (Qco2) was significantly higher in agro-ecosystem which Qco2 increased gradually than other ecosystem which Qco2 decreased step by step with the utilization period. 
3. Soil enzymatic activities improved in different vegetation restoration models. The activity of soil enzyme enhanced which include Phosphatases,invertase, urease, cellulose and catalase, acid phosphtase, catalase and perxidase, while Polyphenol Oxidase weakened with the increasing of years. The abilities of different types of vegetation restoration in improving soil enzymatic activities from high to low was closing hillsides, artificial woodland, abandoned arable land, orchard and terrace. The results of study on the dynamics of soil active organic carbon pool in different vegetation restoration models showed that each fraction of soil organic carbons such as : soil total organic C ( TOC) , microbial organic C (MBC) , water-soluble organic C(WSOC) and microbial Biomass C (MBC) increased with the growing of vegetation. The abilities from high to low were mixed woodland, pure woodland, fallow land and farm land. The same vegetation restoration model has different increaced abilities in each fraction of soil organic carbons.
4. A significant relationship was found between soil microbial biomass, microbial respiration, enzymatic activities, fraction of soil organic carbons and physico-chemical properties and anti-erodibility. The classification and the linear regression models were established on the basis of the analysis of relationship and the frequency of soil involved was analyzed in the dissertation. Based on the soil quality evolvement models established, we estimated the time needed for soil quality to reach to middle level, high level and the climax before vegetation destruction respectively in revegetated grassland, orchard, planted shrub land and planted woodland. 
 5. A large difference in sensitivity of soil property was found. Some soil property including available phosphorous, bio-quality and fraction of soil organic carbons were considered as potential implications. The same rehabilitation model has different kinds and amount of sensitive soil property, while the same soil property has different sensitivity in different vegetation restoration models. EOC, urease, SMBP and soil structure coefficient can be used as implications for ecological rehabilitation. 
6. Through sensitivity analysis, 6 soil bio-quality indicators were identified including SIR, invertase, non-active carbon, SMBN, HWOC, and WOC, which SIR, invertase and non-active carbon were key implications indicators. Soil bio-quality assessment indicators and corresponding assessment model for reflection the bio-quality change of ecological rehabilitation in the hilly gully region of Loess Plateau were established. Seven bio- property index were defined and described such as soil properties indexation, relative soil properties indexation, degradation indexation, restoration indexation, and so on. The linear regression models of bio-quality assessment index were clarified with landuse years in different vegetation restoration models. The regression models for soil quality evolvement were also established. The seven bio- property index had a good practicability and different ecological significance in vegetation restoration, so they can be used as to depict different ecological process.   
Keywords:  Ecological restoration; the Loess hilly regions; Soil Bio-characteristics