Abstract: To investigate the impact of competition on the volume growth of natural mixed-age stands of Yunnan pine, this study, based on 56 sample plots in the southwestern part of Hengduan Mountains in Sichuan, employed four methods (M1, M2, M3, M4) for selecting competitive trees. These methods were combined with four competition indices for modeling variables. Collinearity tests for the modeling variables of the control equation and the full-variable equation were conducted using the nonlinear least squares method. A growth model for natural Yunnan pine stands was constructed, and model selection was performed using F-tests and MSER (Model Selection Estimation Routine). The results indicate that the M3 method for selecting competitive trees was superior to other methods. When combined with the M3 method, the four competition indices (L/M3, H/M3, A/M3, and ME/M3) had MSER values of 0.075, 0.056, 0.169, and 0.200, and R² values of 0.731, 0.735, 0.701, and 0.777, respectively. The growth model constructed with ME/M3 was found to be optimal for the natural mixed-age stands of Yunnan pine. These findings provide theoretical support for the silvicultural management of natural mixed-age stands of Yunnan pine in the region and offer technical methods for achieving subsequent structured management.