Changes in soil microbial biomass carbon and enzyme activity in fluvo-aquic soil of the North China Plain were investigated after the soil, with or without cellulose, was amended with inorganic nitrogen and glucose in the experiment of incubation under constant temperature and humidity. The experiment was designed to have 8 treatments, i.e. control (CK), addition of inorganic nitrogen (N), addition of glucose (G), addition of cellulose (C), addition of glucose and inorganic nitrogen (C+N), addition of inorganic nitrogen in soil with cellulose (C+N), addition of glucose treatment in soil with cellulose (C+G), and addition of glucose and inorganic nitrogen in soil with cellulose (C+G+N). Cumulative soil carbon dioxide release, microbial biomass carbon and activities of dehydrogenase, β-glucosidase, catalase, and alkaline phosphatase were measured, separately at various intervals during the 33 days of incubation. Results show that in all microbial parameters no significant difference existed between CK and Treatment C. As against Treatments CK and C, all the treatments displayed a significant increase in cumulative carbon dioxide release, with Treatment C+G+N listed on the topmost. Treatments G, G+N, C+G, and C+G+N all showed an obvious increment in Cmic content and DHD, APH activity, particularly during the first two weeks of the incubation, while Treatments N and C+N displayed similarly like CK result. The findings implied that glucose could significantly increase microbial activity, but inorganic nitrogen could not. The effects of glucose and inorganic nitrogen on GLU and CAT were not obvious and in most cases no significant difference was found between different treatments. Correlation analysis demonstrates that carbon dioxide release rate was always positively related to APH activity, but not to Cmic and other enzymes activities and their relationships varied with the time of incubation, which was probably due to variation of the composition of soil microbial community or the way soil microbs utilize the substrates with the time of incubation. Cluster analysis further indicates that the 8 treatments could be sorted into three groups according to their soil microbial activity. Treatment C+G+N was the only one in the group of the highest activity, which suggests that it is important to amend the soil containing hard-to-decompose cellulose with inorganic nitrogen and readily available organic carbon at the same time for improving its soil microbial activity.