Abstract: In vitro gas production was used to evaluate for ruminants the fermentation characteristics of mixed oat green hay supplemented with native Kobresia tibetica, Dasiphora fruticosa+Macrophyllous knotweed, and linear leaf Kobresia at ratios of 0∶100, 25∶75, 50∶50, 75∶25 and 100∶0 in the Qinghai plateau. The 48 h gas production and theoretical maximum gas production were positively related to neutral detergent soluble (NDS) content but negatively related to neutral detergent fibre (NDF) and hemicellulose (HC) contents. Gas producing velocity was negatively related to HC content. The lag times were positively related to acid detergent fibre (ADF) and NDF contents, and negatively related to crude protein (CP) and NDS contents. The positive associate effects of different pasture combinations were greater during 12-24 h fermentation, and there was a declining trend of the associate effects as fermentation time increased. When using oat green hay as a nutritional supplement to the ruminants grazing on native grassland, the mixture of oat green hay with the native pastures of K. tibetica, D. fruticosa+M. knotweed, linear leaf Kobresia at a ratio of 50∶50 was appropriate. Therefore, choosing the optimal combination is an effective way to improve the utilization of cold-season pastures of native grasslands in the Qinghai plateau.