An incubation experiment was conducted to study the dynamic response of soil microbial biomass C, N, P in an atrazine-added paddy soil, at a rate of 10 mg/g soil. Results showed that soil microbial biomass C, N, P significantly decreased after addition of atrazine. As composed with control, microbial biomass C, N and P decreased averagely 13.5%,10.1%,20.0%. However, microbial biomass C, N and P significantly increased after application of organic matters and fertilizers. The effect of organic amendments and fertilizers on microbial biomass C, N followed the order of pig manure > Chinese clover> rice straw> NP combined treatment> sole N treatment> sole P treatment. But the effect of organic materials and fertilizers on microbial biomass P was pig manure >NP combined treatment>Chinese clover>sole N treatment> sole P treatment>rice straw.