Soil moisture (SM) and vapor pressure deficit (VPD) are key factors affecting forest carbon stock. However, their effects on forest biomass carbon under hotter and drier climate trends are unclear. These knowledge gaps limit forest management practices and the implementation of climate change mitigation programs. In this study, satellite observations and meteorological data were combined to analyze the asymmetric response of forest biomass carbon to wet and dry changes in China from 2002 to 2020 and identify the relative contributions and influence pathways of SM and VPD on forest biomass carbon under global warming. The results showed that drought did not lead to a decrease in forest biomass carbon but slowed its rate of increase. Excluding the interaction effects of SM and VPD with temperature (Tmp), the dominant effects of SM and VPD on forest biomass carbon differed between dry and wet regions, but the effects of VPD on forest biomass carbon were broader and larger. Notably, the interaction of Tmp and VPD not only amplifies the positive effects of warming on humid regions but also amplifies the negative effects of warming on semi-arid regions, and to some extent offsets the positive effects of warming on sub-humid regions. Additionally, in warming environments, VPD exerts the greatest stress on forest biomass carbon in areas where precipitation (Pre) is 400-700 mm yr-1 and potential evapotranspiration (Pet) is 650-900 mm yr-1. Our results reconcile the contradictions regarding the relative importance of SM and VPD on forest carbon storage and the direction of the influence of VPD on forest carbon sequestration, thereby enhancing our understanding of forest ecosystem carbon cycling in response to climate change.