This study evaluated the effects of nitrogen deposition on soil enzyme activities and microbial community functional diversities (sole-source carbon utilization, SCU) in a Chinese fir plantation subject to simulated nitrogen deposition for seven years at Shaxian State Forest Farm of Fujian Province, China. Nitrogen loadings were designed at 4 levels as N0 (CK), N1, N2 and N3 at the doses of 0, 60, 120 and 240 kg/(hm2·a) N, respectively. Each treatment comprised 3 replicate plots of 20 m×20 m which were sprayed with CO(NH2)2 solutions on the forest floor at the beginning of each month, lasting from January 2004 to the sampling time, March 2010. At the same level of nitrogen deposition, the activities of 6 soil enzymes involving carbon cycle (invertase, cellulose, amylase, β-glucosidase, polyphenol oxidase and peroxidase), the ability of carbon source utilization by microbe, biodiversity and evenness all decreased with the increase of soil depth. At soil depth of 0-20 cm, nitrogen additions promoted cellulose and polyphenol oxidase activities, but inhibited amylase and peroxidase to some extents. High level of nitrogen loading (N3) showed significant positive impact on invertase, but negative on β-glucosidase. Low nitrogen deposition (N1) accelerated the ability of carbon source utilization by microbe, biodiversity and evenness, but moderate-to-high nitrogen deposition (N2, N3) gave the opposite effect. Principal component analysis (PCA) in substrates indicated that the main carbon sources for soil microbes were carbohydrates and carboxylic acid in all treatments and there were significant differences of carbon substrate utilization patterns between treatments. Hence, nitrogen deposition in this experiment accelerated the activities of surface soil cellulose, polyphenol oxidase and invertase, but inhibited amylase, peroxide and β-glucosidase to some extents. Nitrogen deposition produced significant impacts on the functional diversity of soil microbial community in the Chinese fir plantation.