Taking Platycladus orientalis×Ulmus pumila forest (S1), P. orientalis×Prunus davidiana forest (S2), P. orientalis×Armeniaca sibirica forest (S3), P. orientalis×Robinia pseudoacacia forest (S4) and P. orientalis forest (S5), which has same afforestation period and the similar site conditions, in the Guanshan Forest Farm of Renshoushan Province in Beishan of Lanzhou City, as the research object, the ecological stoichiometric characteristics of soil and leaves and their relationship were studied based on field investigation and indoor analysis. The results showed that: (1) The content of C, N and P in the leaves of P. orientalis in different forests followed the order of S4>S3>S2>S1>S5, and the values of mixed forest were all larger than those of pure forests. The value of C∶N in the P. orientalis leaves showed the opposite trend to that of C, N and P content. The value of N∶P less than 14 indicated that plant growth in this area was generally restricted by N elements. (2) The content of soil C, N and P in different forest stands all followed the order of S4>S3>S2>S1>S5, and the values of mixed forests were all larger than those of pure forests. The soil nutrients decreased with the increasing of soil depth, and the "surface accumulation" characteristics of soil nutrients were obvious. C∶N was slightly higher than the national average level of forest soil, and C∶P and N∶P were lower than the national average level, indicating that the soil in this region was insufficient in the supply of N for plant growth. (3) Correlation analysis showed that there is no significant correlation between the changes of C, N and P content in P. orientalis leaves and the changes of C, N and P content of soil in this area, indicating that the supply of soil C, N and P had little effect on C, N and P content of P. orientalis leaves. In conclusion, the P. orientalis mixed forest had better carbon sequestration capacity and nutrient stability than pure P. orientalis forest in Beishan of Lanzhou City. The mixed forests should be constructed reasonably to promote nutrient balance during vegetation restoration in this area.