It is of great significance to study the effects of different slope aspects on soil carbon components and stoichiometric characteristics of carbon, nitrogen and phosphorus in native grass soil, so as to understand the soil carbon fixation and soil organic carbon stability of “Hei Tu Shan” in Three-River Source Region. The mass ratio of soil particulate organic matter ( POM ) and mineral-associated organic matter ( MAOM ), soil organic carbon content of particulate organic matter and mineral-associated organic matter ( SOCPOM, SOCMAOM ), soil total phosphorus content of particulate organic matter and mineral-associated organic matter ( TPPOM, TPMAOM ), soil total nitrogen content of particulate organic matter and mineral-associated organic matter ( TNPOM, TNMAOM ) and ecological stoichiometric ratio were measured in 8 native grasses on shady slope and sunny slope. The results showed that the mass ratio of soil carbon components of 8 native grasses was higher than that of POM, and the content of SOCPOM was lower than that of SOCMAOM. SOCMAOM was significant on the shady slope, and the content of SOCMAOM on the shady slope was higher than that on the sunny slope. Among them, the content of SOCMAOM in different slope aspects was significantly different, and the content of SOCMAOM in Poa pratensis L. cv. Qinghai was more significant than that of SOCPOM. The variation range of TNMAOM content was higher than that of TNPOM, and the TNMAOM content of different grass species was significantly better on the shady and sunny slopes (P<0.001). Among them, the TNPOM and TNMAOM of Poa pratensis L. cv. Qinghai were significantly different on the shady and sunny slopes. The slope aspect had a significant effect on TPPOM and TPMAOM of different native grasses. The TPPOM content of different native grasses on the shady slope was less than that on the sunny slope, and the TPMAOM content of different native grasses on the shady slope was greater than that on the sunny slope. The content of C: NMAOM was higher than that of C: NPOM, and the C, N and P stoichiometry of the four native grasses were significantly different in different slope aspects. Further exploration of the effects of grass species and slope aspect on soil carbon stability may help predict changes in soil organic carbon storage in the future. It is not only helpful to evaluate the degree of grassland degradation, but also to understand the impact of grassland degradation on soil structure and carbon sequestration and provide a scientific basis for the sustainable management of grassland ecosystems.