To investigate the effects of nitrogen deposition on activities of soil enzymes (β-D-glucosidase (βG), Peroxidase (PER), Polyphenol oxidase (PPO), β-N-acetylglucosaminidase (NAG), Acid phosphatase (AP)) involved in carbon, nitrogen, and phosphorus cycles in soils with different moisture content, we conducted a pot simulation experiment in 2017. In the experiment, cuttings of Populus cathayana Rehd were used as plant materials and a randomized block design of two factors (soil moisture and nitrogen deposition) was applied. The soil moistures were 40% (W40), 60% (W60), and 80% (W80) of field capacity, respectively; and nitrogen deposition levels were 0 (N0), 4 (N4), and 8 (N8) g N m^-2 a^-1, respectively. When the soil moisture reached the predetermined moisture content, the simulated nitrogen deposition treatment was started. The soil samples were collected at 6 h, 24 h and 3, 7, 14, 31, and 62 d after nitrogen deposition for the determination of soil enzyme activity. The results showed that the reduction of soil water content decreased significantly the activities of βG, NAG, and PPO, which have the lowest values at W40. Soil moisture had no significant effect on the activities of AP and PER. Nitrogen deposition inhibited the activities of βG, NAG, and AP, and the inhibitory effect was greater with increasing nitrogen concentrations, while it has no significant effect on the activities of PER and PPO. No interaction effect between water moisture and nitrogen were observed on the activities of five soil enzymes. The activities of these five soil enzymes varied greatly at 7 d or 14 d, and then gradually stabilized with the extension of treatment time. During the two-month experimental period, the activities of five soil enzymes in different water and nitrogen treatments showed a "rise-fall-rise-fall" bimodal pattern. This study can provide better understanding for nitrogen deposition effects on the ecological processes of carbon, nitrogen, and phosphorus cycles in forest ecosystem soils under different water conditions, and also supply guidance for forest management.