Microbial activity is rapidly reduced by decreasing temperature, but does not completely cease in the cold season. The deep snow in late winter insulates the soil, further increasing soil temperature and allowing microbes to remain active. Microbes need both carbon (C) and nitrogen (N) for their growth and metabolism and the scarcity of either will limit their activity. Previous results in the lowland and even arctic soils have suggested that continuous extreme C-limitation occurs toward the end of winter. Other studies demonstrated that microbial growth may actually be N-limited. However, whether or not microbial activity on the eastern Tibetan Plateau is limited by energy or nutrients remains unclear. In the current study, the effect of snowpack and nutrient addition on microbial growth and activity in the alpine belt of the eastern Tibetan Plateau was explored, through a field factorial design of litter addition and snow regimes in situ and in laboratory incubation with C and N addition. The results illustrated that labile C was the limiting factor for soil microbial activity and growth in late winter and this situation was strongly demonstrated under a regime with a deeper snow cover.