Distribution of soil organic carbon (SOC) and its affecting factors in four different types of natural grasslands (forest steppe, typical grassland, alpine meadow steppe and desert steppe) in the Loess Plateau were analyzed. Results show that content of soil organic carbon decreases with soil depth, and is significantly higher in 0~20 cm than in 20~40 cm, 40~60 cm, 60~80 cm and 80~100 cm. In the 0~40 cm soil layer, the distribution of organic carbon content in the four types of grasslands tends to be in the order of Alpine meadow steppe > typical grassland > forest steppe > desert steppe; while in the 40~100 cm soil layer, in the order of Alpine meadow steppe > forest steppe > typical grassland > desert steppe. In the Alpine meadow steppe, forest steppe and typical steppe of the Loess Plateau, soil organic carbon is concentrated in the surface layer (0~40 cm), accounting for 71%, 50% and 46% of the total in the profile (0~100 cm), while the distribution is more uniform in the desert steppe; Soil organic carbon content is positively related (p<0.01) to altitude; in the 0~40 cm soil layer, to soil water content (p<0.01); and to total nitrogen (r=0.984 3)；but negatively related to annual mean temperature (p<0.01). Moreover, it has no obvious relationship with annual precipitation in the 100 cm soil layer in all the four types of grasslands.