Abstract: Didymodon vinealis and Bryum argenteum are the two important components of biological soil crusts for sand-ixation at Shapotou region of Northwest China. This paper studied the photosynthetic characteristics of the two mosses during dehydration, and detected the expression of related proteins. Along with the reduction of the mosses water content, the mosses water-oluble protein and chlorophyll contents and the kinetic parameters induced by chlorophyll a fluorescence as well as the photosystem proteins decreased significantly, while the mosses ion leakage and carotenoid contents increased significantly and had positive correlations with the water content. These changes were significantly greater for B. argenteum than for D. vinealis. The results implied that dehydration induced the decrease of the mosses protein contents, the damage of cell membrane, and further, the inactivation of PSII reaction center proteins, resulting in the decline of the mosses photosynthetic capability.