Climate warming has become more pronounced in contemporary times due to the effects of human activities. Alpine meadow is one of the typical vegetation types at high elevations above the treeline on large mountains. Owing to their high-altitude environment, these meadows are sensitive and respond swiftly to climate warming. The community structures of alpine meadows are also significantly affected by climate warming. Most current research, however, has been carried out in high-latitude and high-altitude areas, such as the polar region and the Qinghai-Tibetan Plateau. With regard to subalpine meadows distributed in medium-low-latitude and low-altitude areas, the related studies and conclusions are insufficient. Aiming to reveal the variation of community structure in subalpine meadows in medium-latitude and low-altitude areas under the climate warming, we selected Yunding Mountain, which is the highest peak in the western Shanxi Province, as the study area. Yunding Mountain contains typical subalpine meadows, one of which was selected as the study area in this research. Here, we designed experimental warming plots with 2 amplitudes: small and large. The warming devices were open-top chambers (OTCs) with a small-warming amplitude (OTC₁) and a large-warming amplitude (OTC₂). The OTC heights were 40 cm for OTC₁ and 80 cm for OTC₂. The warming experiment lasted one year. The warming plots were completed in August 2016 and their hydrothermic factors and community structures in the subalpine meadow were measured in July 2017. The results showed that: (1) the air in the meadow was warm and dry in both the small- and large-warming treatments, with corresponding air temperature increases of 3.57℃ and 5.04℃ (P<0.05), and corresponding air humidity decreases of 7.36% and 5.23% (P<0.05). The soil of the meadow trended toward warm and wet, with soil temperatures decreasing by 0.05℃ in OTC₁ and increasing by 0.26℃ in OTC₂ (P<0.05), and soil moisture decreasing by 0.2% and increasing by 0.62% (P>0.05), respectively. (2) Warming had certain negative effects on species diversity in the meadow. However, differences between the treatments were not significant for the species richness index, Simpson's index, and the Shannon's index (P>0.05). This indicates that species diversity of the subalpine meadow is not sensitive to warming. (3) Warming accelerated the growth of grasses and inhibited the growth of forbs in the meadow community, with the different plant functional types transforming from forb to grass with increasing warming amplitude. (4) Redundancy analysis (RDA) ordination and correlation analysis indicated that air and shallow soil temperatures promoted the growth of grass and suppressed the growth of forb; deep soil temperature restrained the growth of sedge; and shallow soil moisture facilitated the growth of grass. In conclusion, warming changed the status of the hydrothermic factors in the subalpine meadow of Yunding Mountain, resulting in an alteration of its community structure, inducing a transformation toward grass.