Abstract: In the spring, summer and autumn of 2016−2017, the field simulated nitrogen deposition test was carried out under the Tianshan Picea schrenkiana forest. Seasonal effects of nitrogen deposition on soil enzyme activities (urea, polyphenol oxidase, peroxidase and invertase) was analyzed and simulated. Provide a basis for studying the effects of nitrogen deposition on ecosystem changes. Results show that nitrogen deposition has a weak effect on soil urease activity and significantly inhibited polyphenol oxidase and peroxidase activities. Medium nitrogen and low nitrogen have a promoting effect on soil sucrase activity, and high nitrogen has inhibitory effect. For the 0−10 cm soil layer, the soil enzyme activity difference is not significant after the simulated nitrogen deposition in spring. The difference of soil enzyme activity in each treatment is significant after the simulated nitrogen deposition in summer and autumn. For 10−20 cm soil layer, only the difference of sucrase and peroxidase activities in each treatment is significant after the increase of simulated nitrogen deposition in summer. After the increase of simulated nitrogen deposition in autumn, only the difference in polyphenol oxidase activity is significant between treatments. High levels of nitrogen deposition may inhibit soil enzyme activity in mountain forest ecosystems in arid regions.