Abstract: The annual variation of wheat litter decomposition fluctuate as mono curve,with biggest value in July.The seasonal variation of 6 enviroment factors are different from wheat litter decomposition in some degrees.The direct effect of microbial biomass,soil animal net number,soil water content and soil temperature on wheat litter decomposition is bigger than other factors.The indirect effect of microbial biomass→soil temperature,microbial biomass→soil water content,microbial biomass→soil animal net number,and soil temperature→animal net number,soil respiration rate→animal net number are more obvious than other ones.

Key words: Qinghai-Tibet Plateau, alpine grassland, soil, N/P ratio.