In order to understand the dynamics of soil carbon in mountain forests with different precipitation gradients, we selected the soil samples of Picea crassifolia and Pinus tabuliformis in Helan Mountains, Luoshan Mountains and Liupan Mountains in Ningxia as the research objects. The vertical and horizontal distribution of soil organic carbon characteristics ［soil organic carbon (SOC), stable carbon isotope composition (δ¹³C) and β value］ in Picea crassifolia and Pinus tabuliformis were analyzed, and the effects of soil chemical indexes on soil organic carbon (SOC) characteristics were investigated by redundancy analysis. We explored the characteristics of soil stable carbon isotopes in arid and semiarid regions, in order to provide a basis for revealing the dynamic change of soil carbon in mountainous forests in arid regions.The results showed that: (1) with the increase of precipitation in the sample land, the soil SOC content of both Picea crassifolia and Pinus tabuliformis increased gradually, while the soil δ¹³C and β values decreased gradually. Under the same precipitation condition, Picea crassifolia was more conducive to soil organic carbon accumulation than Pinus tabuliformis. (2) The SOC content of both Picea crassifolia and Pinus tabuliformis decreased with soil depth increasing, while the δ¹³C of both increased with soil depth increasing. (3) Redundancy analysis between soil organic carbon characteristics and soil chemical indexes of Picea crassifolia and Pinus tabuliformis forests in Helan, Luoshan and Liupan in Ningxia revealed that alkalihydrolyzale nitrogen was the dominant factor affecting soil organic carbon distribution characteristics.