Stand structural complexity and growth partitioning between different tree sizes influence trees competition and resource use efficiency, and thus are closely linked to stand productivity. The main aim of this study was to examine how the stand structure complexity (Gini coefficient Gini) and size-related partitioning of stand growth (growth dominance coefficient GDC and size-growth relationship SGR) temporally changed after different thinning intensities in Chinese fir (Cunninghamia lanceolata) forests, Southeastern China. We analyzed the data of 6 repeated measurements over a nearly 10-year period from a forest thinning experiment with progressively increasing intensity (0, 20%, 25%, 33% and 50% reduction of stand density by selection logging of releasing target trees) and assessed the effects of different thinning intensities using generalized mixed effect model. The thinning intensity of 0 was taken as a control group to identify the stand changes in unthinned stands over time. Size heterogeneity and the relative contribution of larger trees to total stand growth tended to increase as forest grew without thinning management. While the increases in Gini and SGR (excluding between 0 and 0.5) overall negatively influenced the average annual basal area increment of the remaining trees (BAI). Gini in thinned stands decreased during the short term (two years or more) after thinning and the heavy thinning had lower Gini than other treatments several years (eight years or less) after thinning. GDC reduced greater with increasing thinning intensity, and thinning had a significant negative effect on Gini and SGR and a positive effect on BAI. The thinning impacts on BAI increased with the thinning intensity, while the effect magnitudes of different thinning intensities on Gini and SGR were: T50 < T20 < T25 < T33. Overall, thinning increased the stand growth partitioning of small trees, contributing to a uniform stand structure. However, the changes in stand structural complexity and the partitioning of stand growth were related to both thinning intensity and post-thinning time, particularly to thinning intensity. The results provided some implications for designing the intensity and timing of thinning, as well as for determining the size classes of removed trees for different management goals.