The contents of soil microbial biomass carbon(MBC),microbial biomass nitrogen(MBN),microbial biomass quotient value(qMB),respiration intensity and microbial metabolic quotient value(qCO2) in three kinds of alfalfa fields at different soil depths(0-10 cm,10-20 cm) have been preliminarily analyzed through experiments.The results indicat that,in the tilled land with the depth of 0-20 cm,the age for alfalfa growth has effect on the contents of MBC and MBN contained in soil.Comparatively,the field where alfalfa has been planted for four years has maximized content of microbial carbon and nitrogen,followed by one-year cultivated land of alfalfa.The difference is obvious in Microbial biomass quotient value(qMB),respiration intensity and microbial metabolic quotient value(qCO2) between different fields where alfalfa has been planted,relatively,the longer the years of cultivation is,the larger the difference in Microbial biomass quotient value(qMB) and so on between different fields is.Correlation analysis show that soil physical-chemical property affect the microbial characters,in which soil organic matter and total nitrogen have obvious positive relevance with MBC and MBN while negative relevance with bulk density.Without extraneous fertilizer,the quality of the four years alfalfa field is the best in all the alfalfafields relatively.