Moss crust is an important type of desert biological soil crust, which plays an important role in the process of carbon fixation and emission in desert ecosystem. Investigating the long-term impact of nitrogen addition on the photosynthetic physiology and soil organic carbon (SOC) components of moss crust will contribute to a better understanding of the relationship between the photosynthetic characteristics of moss crust and soil carbon sequestration in desert ecosystems, and their regulatory factors. In this study, we studied responses of moss crust formed by Syntrichia caninervis based on a 13a field nitrogen addition experiment in the Gurbantunggut Desert. Three nitrogen treatments were chosen: 0 (N0), 1.0 (N1), and 3.0 g N m^-2 a^-1 (N3), and the prolonged effects of nitrogen addition on the photosynthetic physiology and SOC components of moss crust were conducted. The results indicated that: (1) Compared with the control, the long-term nitrogen addition had no significant effect on the contents of particulate organic carbon (POC) and mineral-associated organic carbon (MAOC) in the crust layer, but significantly reduced the accumulation of POC and MAOC in the 0-5 cm soil depth. (2) The N1 treatment significantly increased the content of chlorophyll and non-structural carbohydrates (NSC), while the N3 treatment significantly reduced the content of chlorophyll a, chlorophyll b, total chlorophyll, and NSC by 50.94%, 42.49%, 46.71%, and 50.85%, respectively. (3) The content of soluble sugars significantly increased under the N1 treatment, while the N3 treatment significantly inhibited their accumulation. The content of proline exhibited a significant decreasing trend with nitrogen concentration, while the long-term nitrogen addition had no significant effect on the content of soluble proteins. (4) Correlation analysis revealed no significant correlation between the long-term nitrogen addition, photosynthetic physiological activity, and POC and MAOC content. However, pH, microbial carbon and nitrogen, conductivity, nitrate nitrogen, and ammonium nitrogen significantly influenced the accumulation of POC and MAOC. In summary, this study reveals the impacts of the long-term nitrogen addition on the photosynthetic physiology and SOC components of moss crust. Moreover, it emphasizes that the response of photosynthetic physiological activity cannot effectively reflect the changes in SOC components, providing data support for understanding the influence of nitrogen deposition on biological soil crust in desert ecosystems.