Soil nitrogen is the main source of crop nitrogen nutrition, and the soil nitrogen support capability hasclosely relation with the nitrogen mineralization. The black soil mineralization of 0~20 cm in Jilin Province and itsinfluencing factors were researched in this article through the original site mineralization testing. The conclusion in-dicated that the inorganic nitrogen was 56.15 kg/hm² in the total maize growing season, in which 24.36 kg/hm² was NH⁴⁺-N, and 31.79 kg/hm² was NO^3--N. In a definite range, the soil nitrogen mineralization increased with the in-crease of temperature and moisture. It was most beneficial to the nitrogen mineralization when the temperature was20~25℃, the water content was about 22%, and soil was drying-wetting alternately. So the temperature and watercontent had obvious positive correlation effect to the speed of mineralization.