Under the different conditions of organic manure and ni trogen fertilizer , the dy namic changet rend of soil oxido reductases activities is studied .Results showed that compared with organic fertilizer or N fertilizer,soil catalase and dehy drogenase activities significantly increased under organic and N fertilizer conditions .With organic fertilizer of 22 500 kg/hm² and N fertilizer of 120 kg/hm², the activities of soil catalase and dehy drogenase were highest , being 1.1750〔0.1 ml/(g·20min)〕and 15.7931 ug/(g·d), respectively .Soil polyphenol oxidase activity decreased with the increase in the amount of organic and nitrogen fertilizer.