In this paper, the effects of planting density, N and P additions, and the both interaction on soil enzyme activity were studied in Acacia auriculiformis stands, which is helpful to provide theoretical basis for the enzyme mechanism affecting soil nutrient transformation under different planting densities, N deposition, and P fertilizer application background in subtropical forests. NH₄Cl and NaH₂PO₄·2H₂O were selected as N and P fertilizers, respectively. Four fertility treatments (control, N, P, and N+P) were used in four density A. auriculiformis stands (low density with 1667 trees/hm², medium density with 2500 trees/hm², relatively high density with 4444 trees/hm², and high density with 10000 trees/hm²). The four fertility treatments were used in 5 small plots of each density A. auriculiformis stand, which formed a total of 16 treatments with 5 repetitions for each treatment. The results showed that the soil urease activity and catalase activity increased in the A. auriculiformis stands after N addition. P addition significantly increased the soil urease activity under high density stand, but reduced urease activity under low density stand compared to that of the control treatment. The activity of soil phosphoric enzyme under N and N+P treatments was significantly smaller than the control and N treatment. The soil urease and phosphoric enzyme activities increased with increasing forest density, while soil catalase activity increased with decreasing stand density under N and N+P treatments, but reduced under the control and P treatment. The interactive effects of different stand densities and N and P additions on the soil catalase, urease and phosphoric enzyme activities were significant in the A. auriculiformis stands.