Abstract: Based on field investigation and experimental data, the variation pattern of above-ground biomass of grasses and its relationships with environmental factors in the small Watershed of Diediegou in Liupan Mountains were studied. The results indicated that there is a significant difference in the biomass of plant communities along environmental gradient, On the Semi-sunny slope,the grass biomass increased gradually with the rising elevation, On the Semi-shady slope and sunny-slope showed: the grass biomass firstly increased and then decreased with the rising elevation;Among slope directions ,the grass biomass on semi-sunny slope is larger than that on Semi-shady slope, and that on sunny-slope is the lowest biomass; The variation of the biomass had a negatively correlation of the layer of 0-20cm, and a positive correlation with soil water content.