Global warming has become an indisputable fact on the Tibetan Plateau in the last decades. Alpine ecosystems are very sensitive to global warming, while the impact may depend on the degree of atmospheric nitrogen (N) deposition. Previous studies paid more attention on year-round warming, while the effects of winter warming was still lacking. In this paper, a manipulative experiment consisted of warming and N addition was carried out in an alpine meadow since 2010, and three types of warming treatments were set up: no-warming (NW), year-round (YW) and winter warming (WW). Warming significantly increased air and soil temperature, but decreased soil moisture. YW significantly decreased ecosystem respiration (Reco) in 2012, and WW decreased Reco under no N addition in 2014, while neither YW nor WW had significant effects on Reco under N addition, indicating that N addition compensated the negative effect of warming on Reco. Annually, YW and WW decreased total carbon (C) emissions, and the decrease extent was even larger under winter warming. Both YW and WW significantly decreased aboveground biomass under no N addition. YW significantly decreased soil inorganic N, and WW decreased it in 2013 and 2014 under no N, and WW decreased soil microbial biomass C. Structure Equation Modelling showed that soil moisture was the most important factors regulating Reco, and soil inorganic N content and microbial biomass C can explain 46.6% and 16.8% variations of Reco. The findings indicate that soil properties changes under warming had substantially effects on ecosystem C efflux in this alpine meadow. Inhibitory effects of winter warming on ecosystem C efflux were mainly attributed to the decline of soil N and soil microbial biomass, thus the effects of winter warming on ecosystem C emission are not so serious as expected and largely depend on N deposition in this semi-arid alpine meadow.