The aim of this study was to assess the initial effects of warming on the community structure and biomass allocation of alpine swamp meadow and alpine meadow, two most widespread ecosystem types in the Qinghai-Tibet Plateau. The air and upper layer soil temperatures were passively enhanced by using open-top chambers (OTCs) with two heights. The air temperature was clearly increased by 2.98℃ in 40cm high OTCs (OTC1) and 5.52℃ in 80cm high OTCs (OTC2) in alpine swamp meadow, and the soil water content decreased by 2.45% (OTC1) and 3.44% (OTC2), respectively. While the air temperature was increased by 2.59℃ (OTC1) and 5.16℃(OTC2) in alpine meadow, and the soil water content decreased by 1.83% (OTC1) and 7.71% (OTC2), respectively. With the warming and drying effects, some changes in the vegetation community structure were observed. The population height, density, coverage, relativity, and important value of each plant community responded differently to warming. In alpine meadow, important values of three species in OTC1 were increased, and five species decreased. The importance values of Saussurea eopygmaea and Primula forbesii decreased significantly, whilethe values of Kobresia pygmaea and Littledalea racemose increased significantly. The warming effects in OTC2 accelerate the development of singularity, the important values of Kobresia pygmaea and Primula forbesii decreased significantly, while the values of Halerpestes tricuspis and Carex atrofusca increased significantly. In alpine swamp meadow, important values of Kobresia tibetica and Kobresia humilis in OTC1 were increased, whilethe values of Ranunculus decreased significantly. The warming effects in OTC2 accelerate the dominances of Kobresia tibetica and Kobresia humilis, and the important value of Ranunculus also increased. Compared to each control plots, warming in alpine meadow caused the coverage of graminoid and sedge decreased, coverage of forbs increased; while in alpine swamp meadow were the reverse. Warming caused the biomass of standing dead and litter in the OTCs were lower than that in the control plots, this means that the warming delayed the senescence and death of plants, and biomass of standing dead and litter in higher warming conditions in OTC2 plots were even less than that in OTC1 plots. The coverage of alpine graminoid and sedge in alpine meadow significantly decreased, while the coverage of forbs increased. In alpine swamp meadow, the coverage of graminoid and sedge increased, while the coverage of forbs decreased. Warming increased the total biomass of both meadows, and higher warming in OTC2 accelerated and prohibited this trend in swamp meadow and alpine meadow, respectively. Warming made the biomass allocation in two meadows transferred to the deeper soil layer to adjust the warming and drying conditions. The four typical species in two meadows further illustrated the community structure and plant growth in response to artificial warming.