[Objective] The improvement degree of soil permeability in the artificial pure forest and mixed forest with different tree species conposition during the growth process was investigated, in order to provide a scientific basis for the selection of tree species during forest construction and during the tending and management of existing tree stands in this area. [Methods] Soil infiltration characteristics based on the double ring infiltration method, including initial infiltration, stable infiltration, average infiltration, and accumulative water quantity, were studied under five different forest types that included Platycladus orientalis, Populus alba var pyramidalis, Robinia pseudoacacia, P. orientalis+R. pseudoacacia, and P. alba var pyramidalis+R. pseudoacacia in the southern and northern mountains of Lanzhou City, Gansu Province. [Results] Soil infiltration characteristics decreased with increasing soil depth in the 0—80 cm soil layer. Soil infiltration characteristics under different forest types followed the order of P. alba var pyramidalis+R. pseudoacacia > P. orientalis+R. pseudoacacia > R. pseudoacacia > P. orientalis > P. alba var pyramidalis, indicating that infiltration characteristics of mixed forests were better than those of pure forests. A common empirical infiltration model provided the best estimates of infiltration processes for the five forest types, followed by the Horton, the Philip, and the Kostiakov models. Soil infiltration characteristics had extremely significant positive correlations with soil water content, total porosity, soil organic matter, soil total nitrogen, and mineral nitrogen. Additionally, soil infiltration characteristics had significant positive correlations with capillary porosity, and noncapillary porosity, and had significant negative correlations with soil bulk density. [Conclusion] These research results would be useful for providing a theoretical basis for the selection of tree species in the construction of artificial forests in the northern and southern mountains of Lanzhou City.