Development of biological crusts result ing from establishment of art ificial vegetation in the desert will significantly change water holding capacity and evaporation process of the soil.An indoor evaporation method was used to study evaporation characteristics of the soils covered with or without biological crusts.Results show that the longer the history of sand dune fixation, the thicker the biological crusts and the sub-soil layer below them, the lower its bulk density, and the higher the soil water holding capacity; which was more significant with moss-crust-covered soil than algae-crust-covered.And so was it in terms of soil evaporation rate after the soils were saturated with water.The process of evaporation, however, could be clearly divided into three stages (p<0.05).In the first stage (constant in evaporation rate), biological crusts contributed to evaporation, but in the second stage (declining in evaporation rate), they inhibited evaporation.Based on analysis, it is held that it is the higher waterholding capacity of the biologic crusts that enhance the possibility of soil water evaporation at the first stage, and inhibit evaporation by holding water in the soil when the soil gets dried up.