The rate of Phytophthora blight of chilli was raised with increase of NO_3-N content in potting experiment. Dynamic variance of bacteria ,fungi and antinomycetes were strikingly affected by NO_3-N content and growth rate of mycelium of Phytophthora capsici Leonian was not germination of spore and sporangium were promoted within 12 hours by high NO_3-N content.