In this paper, Cunninghamia lanceolata was taken as research object in the Experimental Center of Tropical Forestry of Chinese Academy of Forestry, Pingxiang County of Guangxi Province of southern China, we selected the sub-compartments with dominant species of Cunninghamia lanceolata, divided the experimental data into training samples and test samples at 7:3 ratio and established a random forest model with altitude, physiognomy type, slope degree, slope aspect, slope position, soil type, parent rock, soil thickness, humus layer thickness as input variables and growth adaptability of Cunninghamia lanceolata as output variable to predict its adaptability for afforestation sites. At the same time, we analyzed the weight of main site factors on the growth of Cunninghamia lanceolata using the established model. This study showed that the training accuracy of adaptability of Cunninghamia lanceolata based on random forest model was 84. 3% and the generalization accuracy reached 89. 5%. Site factors greatly affecting the growth of Cunninghamia lanceolata were slope degree, slope aspect, the humus layer thickness and altitude, while soil type and soil thickness less affected the growth of Cunninghamia lanceolata. In terms of single site factor, the slopes ranged from 25° to 34° and the altitude greater than 350 m were more suitable for the growth of Cunninghamia lanceolata. The established model based on random forest could deal with complex nonlinear relations and could be applied to make afforestation decision to non-forest lands, then to realize the organic unification of the suitability judgment of Cunninghamia lanceolata with forest land and non-forest land, and the model can be extended to other tree species and provide theoretical support to the problem of matching species with site.