Abstract: To understand the changes of NSC in trees after fertilization, the 15-year-old Fraxinus mandshurica plantation was selected for nitrogen and phosphorus addition in Xiaojiu Forest Farm in Shangzhi City, Heilongjiang Province. The nitrogen and phosphate fertilizer was set at 4 levels（N0:0 g/m~2, N1:5 g/m~2, N2:12.5 g/m~2, N3:20 g/m~2）, and 3 levels（P0:0 g/m~2, P1:7.5 g/m~2, P2:15 g/m~2） respectively. There was a total of 12 treatments of combined application of nitrogen and phosphate fertilizers. The net photosynthetic rate, chlorophyll, total nitrogen, total phosphorus, and non-structural carbohydrate（NSC） concentration of leaves and fine roots were measured at the 3 rd year after fertilization. The results showed that: N and P fertilization led to an increase in the net photosynthetic rate and concentrations of chlorophyll a, chlorophyll b and total chlorophyll of F. mandshurica leaves, and the treatments of N3 P0, N3 P1, N1 P2, N2 P2 and N3 P2 were significantly higher than that of the control. After fertilization, starch and total NSC concentration of leaves were also higher than that of the control, and the treatments of N1 P1, N2 P1, N3 P1, N1 P2, N2 P2 and N3 P2 were significantly higher than those in the control. After fertilization, starch and total NSC concentrations of fine root gradually decreased with the increase of N application, but there was no significant difference from the control. With the increase of nitrogen addition, the leaf nitrogen concentration gradually increased, and N application also promoted the absorption of P, resulting the leaf P concentration of all fertilization treatments was higher than that of the control. N concentration of leaves was positively correlated with the net photosynthetic rate, chlorophyll, starch and total NSC concentration of leaves significantly, while P concentration of leaves was only positively correlated with the net photosynthetic rate and total NSC concentration of leaves significantly. Our results indicate that N and P fertilization could promoted the net photosynthetic rate by improving the N concentration in leaves, which resulted in the increase of NSC in leaves, but the allocation of NSC to fine roots decreased with the improvement of soil N supply.