This study examines asymmetric variations in day-and night-time warming using a least squares linear regression analysis, and characterizes the different effects of seasonally asymmetric warming on vegetation activities in China using a two-order partial correlation analysis method. Using normalized difference vegetation index, vegetation type, and meteorological data, the following results were obtained. (1) There was a significant trend of day-and night-time warming during the growing season from 1982 to 2015. Day-and night-time warming rates were seasonally asymmetric:the day-time warming rate in spring, summer, autumn, and winter was 1.49, 0.98, 0.73, and 1.69 times higher, respectively, than that at night. (2) Day-time warming had a significantly greater and more extensive impact on vegetation than night-time warming. The areas affected by asymmetric seasonal warming in spring and winter were larger than those in summer and autumn. (3) Different vegetation types responded differently to seasonal asymmetry in day-and night-time warming, and the degree of responses varied distinctly between different seasons. This analysis of seasonal variations in day-and night-time warming and the impacts of seasonal warming on different types of vegetation directly contributes to our understanding of the local and regional effects of warming on terrestrial vegetation in China within the context of global climate change.