Two random block experiments were conducted to study the effects of reducing nitrogen and applying organic fertilizers on soil microbial biomass carbon and enzyme activity in the hilly area of central Sichuan basin. The treatments included different types of organic fertilizers and different application rates of nitrogen fertilizers (reducing 20% of nitrogen + without organic fertilizer N1O0, reducing 20% of nitrogen + ordinary organic fertilizer N1O1, reducing 20% of nitrogen + biological organic fertilizer N1O2, reducing 40% of nitrogen + without organic fertilizer N2O0, reducing 40% of nitrogen + ordinary organic fertilizer N2O1, reducing 40% of nitrogen + biological organic fertilizer N1O2). Two control treatments (CK0:No fertilizer; N100: Nitrogen100%) was established in order to study the effects of reducing nitrogen on increasing benefits and raising the utilization efficiency of nitrogen. The results showed that with the decrease of nitrogen fertilizer application rate (N1O0, N2O0), the activities of soil urease, invertase and catalase, and the contents of microbial biomass carbon showed decreasing trends. Compared with N100, the content of microbial biomass carbon was decreased by 25.6 and 35.08 mg/kg at the silking stage; the urease activity was decreased by 11.1% and 14.1%, and the invertase activity was decreased by 30.4% and 97.1% at the big trumpet stage. The yield was decreased by 921.98 and 1 719.62 kg/hm2, respectively. The experiment also showed that using organic fertilizers could increase the activities of soil urease, invertase and catalase, the contents of microbial biomass carbon content and grain yield. Compared with N1O0, the contents of microbial biomass carbon was increased by 38.57% and 54.45%, the activity of urease was increased by 9.73% and 14.82%, the activity of invertase was increased by 42.75% and 64.26%, and the activity of catalase was increased by 11.05% and 11.93%, and the yield was increased 2% and 6% by N1O1 and N1O2, respectively, with N1O2 increasing the yield by 4% more than N1O1. Reducing 20% of nitrogen and using organic fertilizers reduced bare top length, increased spike length, ear rows, 100-kernel weight and grain yield. The correlation between the content of soil microbial biomass carbon, the activities of soil enzyme and the yield was significant or extremely significant. Reducing 20% of nitrogen fertilizer and applying biological organic fertilizer could not only improve maize yield, biomass carbon, soil enzyme activity significantly, but also improve the condition of plant root growth to promote maize yield in the upper dome area under poor siltstone soil conditions.