Abstract: The pot experiments were carried out to study the changes of soil microbial biomass C, N and the clay fixed ammonium using the isotope of 15N during winter wheat growth.The results showed that the soil microbial biomass C increased with the application of organic manure at the begainning of the expriment and then gradually decreased with decreasing of the temperature. At the tillering stage when the temperature gradually increased the soil biomass C rised to the highest value at the anthesis stage, being about 554. 9～794.4mg/kg. The application of organic manure resulted in the highest increase in biomass C amonge the treatinents while that of ammonium sulphate treatment giving the lowest. At the harvest time the soil biomass C decreased to the preplanting level. As the soil biomass C the incorporation of orgariic manure increased the amount of biomass N and reached the highest value among the treatments with the check pot being lowest. Unlike the soil biomass C, the amount of soil blomass N was highest at the three leaf stage of wheat, being about 40. 8～79. 0mg/kg and then decreased with growirig of the wheat and at the anthesis stage decreased to the lowest value arid then increased with the maturing of the wheat.