Forest fire is an important factor affecting the forest ecosystem in the Daxing'anling Mountains. A long-term comprehensive analysis of the changes of subsurface soil nutrients, especially phosphorus and its availability, will contribute to forest fire vegetation restoration management, model simulation and scientific evaluation. Based on historical fire data in Daxing'anling, this study selected 48 plots that were 2-50 years post-fire, at Huzhong, Nanwenghe, Shuanghe, Tuqiang, Tahe, Jiagedaqi, and Mangui, using the neighbouring unburned site, of similar terrain, as the control. Total phosphorus and available phosphorus were determined. A paired t-test, redundant ordination analysis, temporal trend analysis, data average and variation analysis were used to analyse the data. We found that (1) the pooled data mean value showed that total phosphorus and available phosphorus in fire sites were slightly lower than in the control site and the coefficient of variation of the data in burned sites was 37%-49% for two phosphorus forms. This was 6%-22% lower than the non-burned control site. When classifying the data into different rehabilitation times, the paired t-test did not find significant differences, (2) the temporal trend analysis found that total phosphorus first increased and then decreased post-fire (R²=0.89-0.95, P=0.07-0.15), and the threshold values were in 20-30 years. The available phosphorus showed a similar trend, with much lower correlation (R²=0.44-0.67, P=0.44-0.66). However, it was not obvious in the available phosphorus fraction to total phosphorus at the tested period of time (R²=0.08-0.12, P > 0.95), (3) the RDA ordination showed that fire changed the controlling factor for soil phosphorus changes. At fire sites, soil phosphorus variations could be explained by rehabilitation times after fire (15.3%) and longitude (10.7%), while in the control plots, latitude was the most important contributing factor to soil phosphorus change, explaining 27.6% of the variation. Our findings provide important parameters for the management of soil nutrients after forest fires, as well as the ecological assessment of forest fired-induced succession, especially the analysis of soil nutrient changes.