The focus of the research is the minimizing amount of oil sludge via dehydration. The effects of using combination of polyaluminum chloride and biomass as additives on the possible improvement of the dehydration performance (evaluated via water content of oily sludge) of oil sludge and on the yield of pyrolysis oil at 723K were investigated. The main influencing factors of dehydration considered in the experiment are biomass species and dosage, temperature, and flocculation time. The water content of oily sludge was significantly reduced when biomass ranging from 0.5 to 3.0wt% on dosage ratio. The best phase dehydration performance was obtained from Apricot shell of 0.5wt% at 313-323K at flocculate time of 30-40min, while the highest recovery percent of pyrolysis oil (33.54%) was obtained from Walnut shell of 1.0wt%. The results indicate that the positive effects of the biomass in oily sludge on the improvement of dehydration performance and on recovery rate of the pyrolysis oil were observed. The main reasons that the improvement of dehydration performance may be responsible for the mixtures containing different proportions of oil sludge and biomass. The pyrolysis of the mixtures can increase the yield of pyrolysis oil and the higher heating value of oily sludge.