To evaluate the seasonal dynamics of how vegetation restoration in red soil erosion areas of southern China affects soil nitrogen availability, this study focused on different stages of vegetation recovery in typical red soil erosion areas in Changting county, Fujian province (bare land, 10, 20, and 30-year-old Pinus massoniana plantations, and natural secondary forest). Soil samples from the surface layer (0-10 cm) were collected across four seasons to compare the seasonal dynamic characteristics of soil ammonium nitrogen (NH⁺₄-N), nitrate nitrogen (NO^-₃-N), inorganic nitrogen (SIN), dissolved organic nitrogen (DON), nitrogen mineralization rate, microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) contents during vegetation restoration. The results showed that the contents of soil NH⁺₄-N, NO^-₃-N, SIN, DON, MBC and MBN did not significantly improve with vegetation restoration, and there were still significant gaps between Pinus massoniana plantations and zonal natural secondary forests. Soil nitrogen mineralization was mainly shown as ammonification, with weak nitrification. Soil inorganic N was primarily in the form of NH⁺₄-N, and the content of NO^-₃-N was lower. From summer to autumn, soil net nitrogen mineralization values in Pinus massoniana plantations were highest, but they were lower in spring. This indicates that the supply of available soil nitrogen was not balanced. There were highly significant positive correlations between MBC, MBN, and inorganic N components and DON, effectively indicating soil nutrient changes during vegetation restoration. The study implied that soil nutrient restoration was a relatively slow process at southern red soil erosion, with N nutrient supply limitations in the middle and later stages of vegetation restoration. Thus, in the future, we should strengthen vegetation restoration and management to enhance forest productivity and stability, such as employing mixed-species planting models, and applying seasonal N fertilizers according to N requirements.