The Xiaoxing'anling region, a vital forest resource area in China, is instrumental in elucidating the differentiation characteristics of forest carbon density and its influencing factors, which hold significant ecological and climatic implications. This study focused on natural secondary forests across three latitudinal zones—Qinghe, Dailing, and Wuying—within the Xiaoxing'anling region. By employing the plot inventory method, we quantified the carbon density differentiation of various components, including vegetation, plant residues, and soil, and analyzed their influencing factors.Our results revealed substantial spatial variations in vegetation and plant residue carbon density across the study areas. Vegetation carbon density demonstrated a decreasing trend from lower to higher latitudes and increased with the average age of forest stands. Specifically, in Qinghe, vegetation carbon density ranged from 76.22 to 154.57 t/hm2, significantly higher than that in Wuying (74.97 - 105.78 t/hm2) and Dailing (61.49 - 91.89 t/hm2). Notably, the plant residue carbon density in the Korean pine and oak forest plot in Dailing was 6.69 t/hm2, considerably higher than in other regions, whereas the plant residue carbon density in Qinghe and Wuying was relatively lower. No significant differences in soil carbon density were observed across the regions. However, for carbon content, no significant variations were found between latitudes in the surface soil (0 - 10 cm) and middle soil (20 - 40 cm). In contrast, the average carbon content in the deep soil (> 40 cm) of Dailing was 20.56 mg/g, significantly higher than that in Qinghe (3.94 mg/g) and Wuying (11.10 mg/g). However, the soil carbon density among different latitudes had not significant, and the fluctuation range of soil carbon density was 79.03-118.25 t/hm2. The total carbon density of the forest in Qinghe (189.96-235.66 t/hm2) was the highest, while that in Wuying (146.59-182.58 t/hm2) was the lowest. With the increase of latitude, the total carbon density of the forest showed a decreasing trend. The carbon densities of vegetation, soil and residues account for 42% - 64%, 35% - 54% and 1% - 4% of the total carbon density respectively. The carbon density of different mycorrhizal tree species in the Xiaoxing'anling Mountains showed distinct regional characteristics. The carbon density of vegetation was mainly contributed by ectomycorrhizal tree species, accounting for 57% to 99% of the total vegetation carbon density, the proportion of ectomycorrhizal tree species carbon density increased with the increase in latitude, but had decreasing trend with the stand age. Vegetation carbon density was significantly positively correlated with age diversity, basal Area, and maximum tree height. It also showed a marginally significant positive correlation with rainfall and altitude. Plant residues carbon density is significantly positively correlated with rainfall and altitude. Soil carbon density has no significant correlation with any of the factors. Vegetation carbon density is significantly negatively correlated with plant residues carbon density.