Understanding the interrelationships between plant richness and biomass under grazing disturbance is of importance for predicting biomass during different plant growth periods. In this study, we conducted a controlled grazing trail with six grazing intensities in an alpine meadow in the eastern Qilian Mountain from 2012 to 2014. We investigated species richness, lifeform richness, and aboveground and belowground biomass in three grazing seasons (June, August, and October). We analyzed the relationships between plant species richness, lifeform richness, and aboveground and belowground biomass under different grazing intensities. The following results were obtained:(1) Species richness and lifeform richness as well as aboveground biomass were significantly affected by grazing intensity. Species richness was only negatively correlated with grazing intensity in August, whereas lifeform richness showed a single-peak trend in October with grazing intensity. The aboveground biomass was significantly negatively correlated with grazing intensity in different seasons; however, the belowground biomass was not related to grazing intensity. (2) The species richness and aboveground and belowground biomass were significantly affected by the different seasons. The species richness and aboveground biomass showed only a single peak change in the low grazing intensity plot with seasonal changes, and the belowground biomass showed a single peak change in the medium grazing plot with seasonal changes. There was no relationship between lifeform richness and grazing season. (3) There was a significant positive correlation between species and lifeform richness and aboveground and belowground biomass before grazing disturbance. After 3 years of grazing, species richness was positively correlated only with aboveground biomass in August, and lifeform richness was positively correlated with aboveground and belowground biomass in August. (4) Among the different grazing intensity plots, the species richness was significantly positively correlated with aboveground biomass only in the low grazing intensity plot, whereas lifeform richness was positively correlated with aboveground biomass in all grazing intensity plots. In conclusion, grazing disturbed the relationship between plant richness and biomass in alpine meadows, particularly between species richness and belowground biomass. The significant relationship between lifeform richness and aboveground biomass was not affected by grazing intensity. Consequently, lifeform richness showed superiority in determining the biomass in an alpine meadow.