To examine the effects of excessive atmospheric nitrogen deposition on soil microbial carbon and nitrogen in Larix principis-rupprechtii plantation, we conducted fixed experiment plots and 5 years observation experiments to simulate the changes of microbial carbon, nitrogen, and soil respiration in soil of Larix principis-rupprechtii plantation with three nitrogen deposition treatments:CK (N₀:0 g/(m²·a)), light N level (N₁:8 g/(m²·a)), and severe N level (N₂:15 g/(m²·a)) to clarify the response of soil microorganism under excessive nitrogen deposition forest and the influence on soil carbon and nitrogen cycle. The results showed that the average content of soil microbial carbon and nitrogen was 1 098.93 and 97.31 mg/kg. In the May-October growing seasons respectively they showed a downward trend with the increase of soil depth. Light N addition promoted the increase of soil microbial carbon and nitrogen. Severe N addition inhibited the increase of soil microbial carbon and nitrogen. The content of soil microbial carbon and nitrogen increased from May to July and peaked in July, then decreased in August, slightly increased from September to October, and showed an "N" curve. The C/N of soil microbial was between 4.94 and 18.54, and decreased with the increase of N addition. The soil respiration rate of Larix principis-rupprechtii plantation was lower in May and June, continuously increased from July to August and reached the peak in August, then gradually decreased from September to October under different N treatments. The correlation analysis showed that soil respiration was significantly positively correlated with the content of soil total nitrogen, water content, microbial carbon and microbial nitrogen, and was positively correlated with soil organic matter. With the global change, the research results can provide important reference for further clarifying the impact of excessive atmospheric nitrogen deposition on carbon and nitrogen cycle in forest ecosystems.