The rotation period for Cunninghamia lanceolata plantations is set at 25-30 years according to its forest management guidelines. However, subsequent rotations have altered site conditions. Therefore, it is necessary to adopt different thinning measures and rotation periods for various site conditions, in order to optimize the growth rate and stock volume. This study employs the process-based growth model 3-PGmix, categorizing four site quality levels (I, II, III, IV) and simulating two times of thinning (the first at year 10; the second at either year 15 for short interval thinning or year 20 for long interval thinning) with three thinning intensities (light at 10%, moderate at 20%, and heavy at 30%) for Cunninghamia lanceolata plantations in Jinshui and Futian county of Jiangxi province, to identify appropriate thinning measures and rotation periods for different site conditions by comparing the annual maximum growth rate and stock volume of stands. The results showed that: (1) There are significant differences in the annual maximum average growth rate among the different site quality levels, with the highest being 25.09 m³/hm² under site condition I, and the lowest being 8.6 m³/hm² under site condition IV. (2) The optimal rotation periods for the four site quality levels of unthinning forest stand are 17.7 years, 18.7 years, 21.6 years, and 25.4 years, respectively, and the stand stock volume decreased with the increase of rotation period. The rotation period of thinning stands decreased with the increase of site grade and increased with the increase of thinning intensity. (3) The effects of different thinning measures on forest stock are different under different site conditions. From maximizing forest stock, long-interval thinning outperforms short-interval thinning. For site quality level I and II, the optimal thinning method is 20% initial thinning and 30% secondary thinning. For site quality level III, it is 10% for the initial thinning and 20% for the secondary. According to the simulated rotation period, the optimal thinning period is 28.5 years, 29.4 years and 30.9 years, which can maximize stock volume. The improvement of soil fertility should be the main concern for the forest stand with site quality level IV. The simulation results of this study can provide valuable reference for adjusting thinning measures and rotation periods under different site quality levels, thereby contributing to the refined forest management and quality improvement of Cunninghamia lanceolata plantations in China.