The balance and stoichiometry of carbon (C), nitrogen (N), and phosphorus (P) can reflect the quality and content of organic matter and is very important for understanding ecological processes and ecosystem response to climate change and disturbance. To explore the spatial distribution characteristics of C, N, P, and their stoichiometry of topsoil in Sanjiangyuan (SJY), we sampled 0-20 cm soil of alpine grassland in SJY, measured soil C, N, and P, and analyzed their correlation with latitude, longitude, altitude, and vegetation characteristics (diversity, height, coverage, biomass, etc.). The results showed that the average densities of soil organic C (SOC), total N (TN), total P (TP), and soil inorganic C (SIC) in SJY were 7.56 kg·m^-2, 0.71 kg·m^-2, 151.57 g·m^-2, and 1.77 kg·m^-2, respectively. The spatial distribution of SOC, TN, and TP in SJY showed a pattern of high in the east and low in the west, while SIC showed the opposite pattern. The heterogeneity of soil TP in the SJY region was small, which indicated that there may be little difference in soil parent materials in the whole region. The soil nutrients were mainly affected by longitude, soil water content, pH, and vegetation height and coverage. The C: N: P ratio of the 0-20 cm soil in the study area was approximately 48:5:1, and the C: N, C: P, and N: P ratios were significantly affected by soil water content and vegetation height. Soil C: N ratio (10.45) and N:P ratio (4.51) were lower than the national level, which indicated that the soil N mineralization capacity of SJY was higher than that of other regions in China, and the degree of soil N limit was small.