泥石流易损度是指在一定区域和给定时段内，由于泥石流灾害而可能导致的该区域内所存在的一切人、财、物的潜在最大损失。易损度评价因子主要分为财产指标和人口指标两大类。财产指标包括建筑资产、交通设施资产、生命线工程资产、个人财产和土地资源；人口指标包括人口年龄、受教育程度、富裕状况、人口自然增长率和人口密度。财产指标和人口指标包括人口年龄、受教育程度、富裕状况、人口自然增长率和人口密度。财产指标和人口指标具有不同的计量单位因而不能直接相加。本文指出的“转换赋值函数”解决了人、财、物统一标度和综合表达的难题，使泥石流易损度定量表达为财产指标转换函数赋值与人口指标转换函数赋值之和的二分之一的平均根。易损度取值范围介于0－1或0％－100％之间。

Debris flow vulnerability is the potential maximum losses in people, property and materials due to potential debris flow damaging phenomenon for a specified area and during a reference period, which is measured on a scale of 0 (0%) to 1 (100%). Debris flow vulnerability is related to the huge and complex socioeconomic and environmental system, which is mainly classified into two categories of property and population. The property index includes the assets of building, transportation infrastructure, lifeline, personal property, and land resources. Site-specific debris flow vulnerability is a complex-function of the property index. The population index includes the age, education level, wealth situation, natural growth rate of population, and population density. Site-specific debris flow vulnerability is a sum-production-function of the property index. Monetary unit is used to measure the property value, while the value of person may not be simply measured by money. Thus the property index and population index with different units cannot be directly added. In this paper, the transformation functions have successfully provided identical scale and dimensionless expression for both the indexes of property and of population, which make the vulnerability possibly to be expressed synthetically as the sum of the values of property and population. Mathematically debris flow vulnerability is compouted by the square root of the half sum of the transformed values of property index and population index.