Objective To study the effects of different competition levels and topography on the canopy length and compare the forest layers, the crown ratio model considering competition and topographic (slope, slope aspect and slope position) variables of Pinus koraiensis plantation in eastern area of Liaoning province was developed.

Method The crown ratio model was developed by incorporating competition index and topographic variable using re-parameterization and dummy variable methods. and the specific topographic variable expressing the largest contribution was selected. The effect of competition and topographic variable on the crown ratio was simulated.

Result Compared with the basic model, the R²_a for the finial model incorporating competition, topographic variable and forest layer increased by 0.113, RMSE decreased by 0.012. The contributions of competition, slope aspect and forest layer to the crown ratio model were 14.14%、2.25%、0.16%, respectively. The crown ratio decreased with the increase of D and increased with the increase of forest competition. With the increase of the competition, the crown ratio turned from negative growth to positive growth with tree height increasing gradually . The F test showed that there were significant differences in crown ratio between different slope aspects and forest layers, and the change rule was shady slope > semi-sunny slope > sunny slope and upper forest layer > lower forest layer.

Conclusion Topography and forest competition factors significantly affect the crown ratio, and slope aspect is the most important topographic factor affecting the crown ratio of individual tree of Pinus koraiensis plantation. The crown ratio model based on topography and forest competition has high accuracy and provides a reference for the management and growth prediction of Pinus koraiensis plantation in eastern area of Liaoning Province.