For revealing the effects and mechanism of dissolved organic matter (DOM) accumulation in soil during the restoration process of soil and water conservation forests, the dynamics of dissolved carbon and nitrogen content and its organic composition characteristics was analyzed in the surface soil. The soils were collected from three typical kinds of forestlands:Caragana korshinskii, Robinia pseudoacacia and abandoned land, which have been established for 12 to 45 years, and changes in soil dissolved carbon and nitrogen content, three-dimensional fluorescence characteristics and parameters were determined. The results showed that the contents of dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) in the three vegetation soils increased significantly with recovery duration. Under the same recovery period, the contents of DOC, DON and DIN generally appear as abandoned land < Caragana korshinskii < Robinia pseudoacacia. However, the ratios of DOC to SOC, DON to TN and DOC to DON in Caragana korshinskii and Robinia pseudoacacia did not increase continuously. After 45 years, the ratio of DOC to SOC and DOC to DON were the highest in abandoned land and the lowest in Robinia pseudoacacia. The ratio of DON to TN was the highest in Robinia pseudoacacia, while the lowest in abandoned land. Three-dimensional fluorescence spectroscopy combined with parallel factor (EEM-PARAFAC) analysis showed that the dissolved organic matter (DOM) in all plots mainly consists of 4 components:macromolecule humus (C1), fulvic acid (C2), tryptophan-like (C3), and humus substance related to human activities such as manure (C4). The C1 component has the largest proportion, with an average proportion of 37.4%. With the extension of the restoration period, the proportion of C3 component in soil DOM of the three vegetation types increased, the proportion of C2 and C4 components decreased, the proportion of C1 component increased in Caragana korshinskii and Robinia pseudoacacia forests and decreased in abandoned land. The DOM fluorescence index (FI), freshness index (β:α), and biological index (BIX) of all plots were not significantly different. The average fluorescence index of each plot was 1.63, the average freshness index was 0.58, and the biological index was 0.59. The humification index (HIX) of abandoned land at different restoration years has no difference. The humification index of Caragana korshinskii and Robinia pseudoacacia forests are significantly higher than the abandoned land. The humification index of Caragana korshinskii forest restored 45 years and 28 years was significantly higher than that of restoration 18a, and the humification index of Robinia pseudoacacia forest restored 45 years and 18 years was significantly higher than 12 years. In conclusion, the continuous restoration of soil and water conservation forests significantly increased the content of soil dissolved carbon and nitrogen, and result in more stable and complex composition of dissolved organic matter, which is conducive to continuous accumulation, especially in the Robinia pseudoacacia forestland.