Soil aggregation as one of the key processes can maintain soil quality. Revealing the relationships of soil aggregate stability with the relevant bio-chemical parameters could provide valuable guidance to maintain soil quality in the Chinese fir plantations. In this study, soil samples (0–20 cm and 20–40 cm depths) were collected from Chinese fir plantations with various stand ages (3 years, 9 years, 17 years, and 26 years) in Guangxi, China. Soil aggregates with four different sizes were obtained through the optimal moisture sieving method, including the >2 mm, 2-1 mm, 1–0.25 mm, and <0.25 mm fractions. For each fractions, the organic C (OC), total N (TN), microbial biomass C (MBC), microbial biomass N (MBN), and microbial respiration rate (MRR) were measured. Regardless of the Chinese fir plantation age, soil OC and TN contents were concentrated in the <0.25 mm fractions, while soil MBC, MBN, and MRR were relatively high in the 1–0.25 mm fractions compared with other fractions. Soil mean weight diameter (MWD) and geometric mean diameter (GMD) were higher in the 17-year Chinese fir plantations than other stand ages, which indicated stronger stability of soil aggregates in the 17-year Chinese fir plantations. In the process of Chinese fir planting, the peaks of soil OC, TN, MBC, MBN, and MRR were observed in the 17-year Chinese fir plantations. Based on the redundancy analysis (RDA) and Pearson's correlation analysis, soil aggregate stability was significantly positively correlated (P < 0.05) with the OC, TN, MBC, and MBN over time, particularly in the OC, which was the most important contributor of the chronological variation in soil aggregate stability. Overall, soil aggregate stability and aggregate-related OC, TN, MBC, and MBN are the highest in the 17-year Chinese fir plantations. With the growth of Chinese fir after 17 years, these factors decrease significantly. Therefore, it is necessary to adopt reasonable management methods (i.e., appropriate application of organic manure) to increase soil aggregate stability and maintain soil quality in Guangxi, China.