It is of great interest to elucidate the biogeographic patterns of soil microorganisms and their driving forces, which are fundamental to predicting alterations in microbial‐mediated functions arising from environmental changes. Although the vertical movement of dissolved organic matter (DOM) drives the cycle of nutrients such as soil carbon, in the restored ecosystem, the relationship between DOM and soil microbial nutrient utilization remains to be determined. Here, we investigated the changes of soil microbial community at 0–40 cm depth profile in three stages (10, 30, 50 years) of succession in Larix olgensis plantations and the fluorescence spectrum composition of DOM. With the increase of soil depth, the signal source of microorganisms increases. In a coniferous forest soil environment, the possible main source of DOM in deep soil is the production of microbial metabolism. Difficulty in the decomposition of organic matter determines the distribution and composition of microorganisms. Increasing forest age makes bacteria and fungi more specific and bacterial‐fungal associations greater. Overall, our work contributes to the understanding of factors underlying microbial community distribution in plantation forests and the importance of DOM quality in the building microbial community.