Abstract: To make clear the effects of different concentrations of nitrogen and soil moistures on soil nitrification and microbial characteristics, especially the responses to high nitrogen concentration, nitrification, microbial biomass carbon and microbial community diversity in red paddy soils were studied under four ammonium sulfate doses 0(CK), 120 mg(N)·kg^-1 (A1), 600 mg(N)·kg^-1 (A2), 1 200 mg(N)·kg^-1 (A3) and adjusted soil moistures of 40%, 60% and 80% of water holding capacity (WHC). Nitrification ratios and rates of A2 and A3 treatments were generally low under 40%, 60% and 80% WHC. Nitrification ratios and rates of A1 treatments significantly increased with increasing soil moisture. Nitrification significantly decreased with decreasing ammonium sulfate at constant soil moisture. Soil microbial biomass carbon reduced with increasing ammonium sulfate from 40%, 60% to 80%WHC. The trend in microbial biomass carbon at constant ammonium sulfate concentration was 60%WHC > 80%WHC > 40%WHC. No interactive effects were noted in the soil moisture and ammonium sulfate treatments. For different concentrations of nitrogen and soil moistures, BIOLOG analysis showed that AWCD value and Shannon, Simpson, McIntosh indices were highest under A1 treatment at 60%WHC, followed by CK treatment at 60%WHC. For different soil moisture, excessive fertilization led to low microbial activity. AWCD value and Shannon, Simpson, McIntosh indices were low under A2 and A3 ammonium sulfate treatments. The findings suggested different soil biological and biochemical properties under different concentrations of nitrogen and soil moistures. Overuse of chemical fertilizers did no enhance soil biological properties and biochemical function.