In order to explore the effects of different thinning intensities on soil carbon and nitrogen fractions in Chinese fir plantation, this study was conducted in 11-year-old fir plantations in Guanzhuang state-owned forest in Sanming City, Fujian Province. Three types of thinning, including light intensive thinning (LIT), moderate interval thinning (MIT), and hight intensive thinning (HIT) were adopted. The variations of total organic carbon (SOC), total nitrogen (TN), readily oxidized organic carbon (ROC), nitrate nitrogen (NO₃-N), ammonium nitrogen (NH₄⁺-N), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial entropy carbon (qMBC) and microbial entropy nitrogen (qMBN) in the 0-10,10-20,20-40,40-60,60-80,80-100 cm soil layers of different thinning intensities were explored. The results showed that thinning reduced soil SOC and TN contents by 1.4%~36.9% and 3.1%~45.7%, respectively. Thinning increased soil MBC and NO₃-N content, while the change degrees on ROC, NH₄⁺-N and MBN showed differences in different soil layers. With the increase of thinning intensity, the values of qMBC and qMBN gradually increased. Correlation analysis showed that soil SOC was significantly positively correlated with TN, qMBC, ROC, NH₄⁺-N, MBC and MBN, respectively (P<0.01). TN was significantly positively correlated with qMBN, ROC, NH₄⁺-N MBC and MBN (P<0.01). The thinning treatment of Cunninghamia lanceolate plantation decreased SOC and TN content in soil surface layer, increased SMBC content and qMBC, qMBN value in soil, and increased SMBN content in soil surface layer (0-10 cm). The results indicate that the decrease of soil SOC and TN content caused by thinning is mainly due to the increase of active carbon and nitrogen content, which improves the decomposition rate of organic matter in soil, and finally leads to the decrease of soil SOC and TN content.