Abstract: To evaluate the role of net mineralized nitrogen (N) in the N supply capacity and provide theoretical basis for rational fertilization, the effect of combined application of N fertilizer and manure on the dynamic changes of net mineralized N content and net N mineralized rate were studied in greenhouse soil. A tomato field fertilization experiment with eight treatments of different N fertilizer (N0, N1, N2 and N3) combined with different manure (MN0, MN1, MN2 and MN3) was conducted for seven consecutive years in greenhouse. The net mineralized N and net N mineralization rate were measured under indoor aerobic cultivation method, followed by the analysis of the relationship between soil net mineralized N and soluble organic N (SON), microbial biomass N (MBN). The results showed that the contents of soil total N (TN) and inorganic N (N_in) with combined application of N fertilizer and manure were significantly higher than that with single application of N fertilizer (P < 0.05) in the 0-20 cm soil layer. The N application rate had no significant effect on TN, but it had significant effect on N_in, showing a significant increase trend with the increase of N application rate. The net mineralized N of each treatment increased gradually first and then decreased with the prolongation of incubation time. The soil net N mineralization rate of each treatment reached the maximum in the 7^th day of incubation, and decreased rapidly during 7-70 days. After 70 days, it showed a slow decreasing trend. Soil net mineralized N and net N mineralization rate under the treatments of combined application of N fertilizer and manure were significantly higher than that of single application of N fertilizer (P < 0.05), indicating a downward trend with the increase of N application rate. The treatments of combined application of N fertilizer and manure significantly increased the contents of SON and MBN compared with single application of N fertilizer (P < 0.05), but there was no significant effect induced by N application. The net mineralized N was closely related to SON and MBN. In summary, the treatments of MN1 and MN2 could significantly increase soil N supply capacity (inorganic N + net mineralized N). Under the greenhouse conditions of tomato cultivation, the combined application N fertilizer and manure for seven consecutive years could significantly improve N supply capacity of greenhouse soil to better coordinate the soil N supply and immobilization.