Abstract: The soil total nitrogen,soil microbial biomass nitrogen and their relationship of three types of soils on the Loess Plateau(Ust-Sandiic Entisols at Shenmu,Los-Orthic-Entisol at Yan'an and Eum-Orthic Anthrosol at Yangling) were investigated to determine how they were affected by location and soil depth(0200 cm) on the Loess Plateau.The results showed that the contents of soil total nitrogen and microbial biomass nitrogen were significantly different in different situations and soil depth.From south to north on Loess Plateau,the contents of soil total nitrogen and microbial biomass nitrogen decreased significantly.At the same location,the contents of soil total nitrogen and microbial biomass nitrogen in the profiles decreased remarkably within 0-60 cm,decreased slightly within 60-120 cm and remained at the lowest level under 120 cm.Soil microbial biomass nitrogen was significantly correlated with soil total nitrogen,soil organic carbon and soil microbial biomass carbon(P0.01).The range of soil microbial biomass nitrogen and soil total nitrogen ratio was 0.42%9.44%.Land use was not closely related with the contents of soil total nitrogen and soil C/N(P0.05) except soil microbial biomass nitrogen and the ratio of soil microbial biomass nitrogen over soil total nitrogen(P0.05).The contents of soil microbial biomass nitrogen and the ratio of soil microbial biomass nitrogen over soil total nitrogen in grassland soil was slightly higher compared with farmland.The results indicated that the soil microbial biomass nitrogen and the ratio of soil microbial biomass nitrogen over soil total nitrogen reflected the variation of soil quality more effectively.