Chinese fir (Cunninghamia lanceolata) is an important fast-growing tree species in southern China. Simultaneously, nitrogen (N) deposition amounts are increasing in southern China. However, the effect of increasing atmospheric N deposition on arbuscular mycorrhizal fungal (AMF) colonization and glomalin-related soil protein (GRSP) in Chinese fir plantations remains poorly understood. Therefore, we conducted a N addition (N3: 3g N m^-2 a^-1, N6: 6g N m^-2 a^-1, and Control: 0 g N m^-2 a^-1) experiment in a ten-year-old Chinese fir plantation; AMF colonization and GRSP concentrations were evaluated in January and April, 2019. The results showed that in January, compared with the control treatment, the N3 treatment significantly increased the AMF colonization. The N6 treatment significantly increased the concentration of easily extractable GRSP (EE-GRSP) relative to the control treatment. Nitrogen deposition had no significant effect on concentrations of total GRSP (T-GRSP). In April, compared with the control treatment, the N3 treatment significantly increased the AMF colonization, but significantly reduced concentrations of EE-GRSP. The N6 treatment significantly increased the concentration of T-GRSP, but significantly reduced that of EE-GRSP. Under the same N addition rate, the AMF colonization in April was significantly lower than that in January, and the concentrations of EE-GRSP and T-GRSP showed a contrasting trend. Soil available phosphorus was significantly negatively correlated with AMF colonization but positively correlated with the concentrations of EE-GRSP and T-GRSP. AMF colonization, and concentrations of EE-GRSP and T-GRSP were significantly positively and negatively correlated with pH, respectively. Our results provided new insights in understanding the symbiotic relationship between Chinese fir and AMF under N deposition.