Predicted warming is considered to intensively affect plant community structure and function in Qinghai-Tibet Plateau, and available soil moisture could mediate the responses of alpine plant community to climate warming. However, many studies have focused on the effects of climate warming alone on single alpine ecosystem, less was known what effects of climate warming will have on community with different soil moisture. Plasticity of root functional traits plays an important role in plant growth and survival under changing climate, reflects the utilization strategy of soil resources. Thus, we used open top chambers (OTCs) to artificially warm two different plant communities in Qinghai-Tibet Plateau from 2012 to 2016. We harvested root biomass, measured root length, diameter, area, and root carbon, nitrogen concentrations in both alpine meadows with different soil moisture. The results showed that (1) warming significantly increased root biomass at the depth of 0-10 cm and 0-20 cm in the alpine meadow, but didn't change root biomass in the swamp meadow. (2) Warming significantly increased root tissue density at the depth of 0-10 cm and 10-20 cm in the alpine meadow, but significantly increased specific root length and specific root area at the depth of 10-20 cm in the swamp meadow.(3) Warming remarkably decreased root nitrogen concentration at depth of 10-20 cm and root carbon concentration at the depth of 0-10 cm and 10-20 cm in the alpine meadow, but increased root carbon at the depth of 0-10 cm and 10-20 cm as well as nitrogen concentrations at the depth of 10-20 cm in the swamp meadow. Moreover, warming significantly increased root carbon:nitrogen ratio at the depth of 10-20 cm in both alpine meadows. The present results indicated that warming may promote the Kobresia pygmea meadow with lower soil water content to develop conservative strategy so as to adapt the warmer and drier environment, as well as promote the Kobresia tibetica swamp meadow with ample soil water to develop acquisitive strategy to promptly utilize soil nutrients for plant growth in future. Generally, our results suggested that soil water could mediate effects of climate warming on alpine meadows, emphasizing the importance of soil water under future warming in the study region.