Abstract: Dynamics of soil fixed NH₄⁺ and microbiomass N in the growing season of winter wheat were studied by field experiment．The results show that the soil fixed NH₄⁺ increases significantly after the application of basal fertilizer，decreases significantly after spring and reaches to the lowest point at flowering stage It reaches nearly the same level before harvest as that of sowing period because the soil fixed NH₄⁺ pool is complemented by nitrogen mineralization in the late crop growing stage when crop has a low nitrogen uptake．Soil microbiomass N changes with the seas0n．It has a slight increase in short period after the application of basal fertilizer and a second increase after the application of spring fertilizer，reaches to the lowest point at the flowering stage and is recovered in the latest stage because of lower crop N uptake．