Abstract: The substrate cultivated pepper（Capsicum annuum L.‘Longjiao 10’）in greenhouse used as test material，the experiment was conducted to study the effects of different water and nitrogen supply on the number of nitrogen transformed bacteria and the activities of related enzymes. Three water levels （80%，60%，40% of water-holding capacity in the substrate）and applied urea levels（0，2 989.83，1 993.12，996.72 kg ? hm-2）were randomized complete block designed. The results showed that increasing urea application rate increased the number of ammonifiers but decreased the number of nitrifying bacteria and denitrifying bacteria in substrate，having no regular effect on nitrite bacteria. Moreover，the nitrogen transformation bacteria number reached the highest when substrate relative moisture content was 60% of field capacity. The moderate water and nitrogen supply was conductive to improving urease and cellulase activity in substrate. However，the increase of water and nitrogen supply was beneficial for improving substrate sucrase activities. Reducing the water supply was conducive to improving the activities of catalase and urease under low nitrogen conditions. The activities of urease and sucrase had significantly positive correlations with the number of ammonifiers，nitrifying bacteria and nitrite bacteria. Cellulase activity had significantly positive correlations with the number of ammonifiers，nitrifying bacteria，nitrite bacteria and denitrifying bacteria. Catalase activity had significantly negative correlations with the number of ammonifiers and denitrifying bacteria. A reasonable mix of moisture and nitrogen can increase the yield of pepper. 60% substrate relative moisture and 2 989.83 kg ? hm-2 urea supply had the highest level of nitrogen transformation bacteria，activities of related enzymes，and yield.

Key words: pepper, water and nitrogen supply, substrate microbes, substrate enzyme, correlation analysis, yield