Microorganism plays an important role in litter decomposition, and the change of microbial biomass is of ecological significance in understanding the mechanism of litter decomposition in the forest ecosystem. In order to understand the dynamic characteristics of microbial biomass during litter decomposition process in the Qinghai spruce forest, Qilian Mountains, we collected leaf litter samples at the crown center (CC) and crown edge (CE) by decomposition litterbags in different times (the early growing season and the late growing season) and altitudes (i.e., 2850 m, 2950 m, 3050 m, 3150 m and 3250 m). The temporal and spatial changes of microbial biomass carbon (MBC), microbial biomass nitrogen (MBN) and microbial biomass phosphorus (MBP) in litter and soil were analyzed. Temporally, the MBC, MBN and MBP increased in the early growing season and decreased in the late growing season. On the contrary, the MBC, MBN and MBP in soil decreased in early growing season and increased in late growing season. However, the content of MBP in soil at CE of 3050 m altitude and 3250 m altitude showed an inverted "N" shaped pattern, that is, "decrease-rise-decrease". Spatially, the contents of MBC and MBN in litter were higher than those in soil at all plots, but MBP was the opposite. The contents of MBC, MBN and MBP at the CE were significantly (P<0.05) higher than those at the CC. In general, the contents of MBC, MBN and MBP were the highest at medium altitude (P<0.05), followed by low altitude, and then the lowest at high altitude (P<0.05). The results would lay foundation to understand the process and mechanism of litter decomposition in the alpine mountain forest ecosystem, and further understand the structure and function of the ecosystem.