Abstract: Field and incubation experiments were conducted with eumorthic anthrosols to study the dynamic change of soil microbial biomass nitrogen as well as the influence of soil moisture and temperature.Field trial showed that soil microbial biomass nitrogen was the highest in summer and hiher in spring and autumn,where as middle at the beginning of winter and lowest in the hard period of winter,and there existed very significant of significant positive correlation between microbial biomass nitrogen and soil temperature,the correlation coefficient of which was over 0.855.In the period of field experiment,the soil water content was enough for microorganism activity,so there was no relationship between microbial biomass nitrogen and soil water.The results of incubation experiment revealed that in the range from 4℃ to 36℃,the soil microbial biomass nitrogen increased with temperature increase,both of which had a significant linear relationship.It was another story for relation of soil moisture to soil microbial biomass nitrogen:the microbial biomass nitrogen increased with moisture in the range from 6.7% to 11.0% while maintaining stable when soil moisture varied from 10.9% to 23.2%,and the correlation equation between soil microbial biomass nitrogen (BN) and soil water content 9x) was BN=74.679e-0.0588/x(r=0.956*). The microbial biomass nitrogen decreased dramatically with frequent wettingdrying alternation and hardly changed with freezing-thawing alternation.