In this study, an indoor soil culture experiment simulating the oxygen-deficient environment of Phyllostachys praecox forest with mulching was set up to explore the effects of soil hypoxia (oxygen content in 0%, 5%, 10%, and 20%) on nitrogen transformation, related enzyme activities and soil microbes. The results showed there was a pronounced impact of oxygen content on soil inorganic nitrogen levels. Under 0% and 5% oxygen levels, a significant decrease in soil NO₃^--N content was observed, accompanied by an increase in NH₄⁺-N accumulation at the end of the incubation period. Meanwhile, urease activity was suppressed but nitrate reductase and nitrite reductase activities were enhanced. Incubation under 0% oxygen led to a notable reduction in soil microbial biomass carbon by 16.79% and microbial biomass nitrogen by 13.25% compared to non-anoxic settings. The diversity of soil microbial community decreased with the decreasing oxygen level, although 5% oxygen content resulted in an enhanced microbial community diversity. Furthermore, although the dominant phylum and genus of soil microbial community remained consistent across varying oxygen contents, there were significant differences in their relative abundances. Overall, this study illustrates that soil hypoxia in Phyllostachys praecox forest can induce alterations in soil nitrogen composition, enzyme activity, and microbial community, which is not benefical for the transformation and utilization of soil nitrogen, ultimately raising the risk of soil nitrogen loss, which is detrimental to the growth and management of Phyllostachys praecox forests.