It is one of important parameters that soil microbial biomass carbon and nitrogen（SMB-C and SMB-N） in plant nutrition and soil fertility. The experiment under incubation and pot experiment with spring wheat were conducted to evaluate SMB-C and SMB-N respectively under the treatments of polyaspartic acid（PASP），urea（U） and polyaspartic urea （PASPU）. The incubation results showed that PASP could enhance the amount of SMB-C and SMB-N at the early stage dur- ing incubation period. Comparing with urea treatment， PASPU significantly increased the amount of SMB-C and SMB-N. In- cubation results at period of first 45 days showed that the SMB-N under U treatment decreased the amount of N 21.87 mg? kg-1 soil and the SMB-N under PASPU treatment only N4.8 mg?kg -1 soil. The SMB-N under PASPU treatment from pot experiment was N 12.57 mg?kg-1 soil lower than the one of U treatment at the trefoil stage of spring wheat and N 2.85 mg ?kg-1 soil higher at the maturity. The amount of SMB-C under PASPU treatment was C 16.12 mg?kg-1 soil and C 14.81 mg?kg -1 soil lower respectively at the heading and maturity stage than the one under U treatment. It means that PASPU could have more efficient nitrogen than urea to be used during the period of crop growth since N nutrient released from PASPU last longer than ones from the urea due to PASP capture more available nitrogen from PASPU.