Microbial populations at different soil depths in the different vegetation soils of the Mizhi county on the Loess Plateau were studied. The results showed that (1) in this region, the amount of soil microbes was abundant and the proportion of Caragana korshinskii was much larger than others. It was least under Medicago sativa L. However, the different proportions of bacteria, fungi and actinomycetes in a plot was obvious and in the order: bacteria> actinomycetes> fungi. (2) The quantity of actinomycetes and fungi clearly decreased with the soil depth, however this was not obvious for bacteria. (3) The quantity of microbes under the naturally vegetated slope was larger than under than annual Medicago sativa L. grassland. The quantity of microbes under the bush vegetation- Caragana korshinskii- was more than under tree forest- dominated by Prunus armeniaca,Robinia Pseudoacacia,Platrhadus orientalis and Ziziphus jujube. The quantity of microbes under fruit tree plantations, (Prunus armeniaca) , which also supported grass, was greater than under the forest, Platrhadus orientalis, and Robinia pseudoacacia, pure grassland, Medicago sativa L. and fruit tree plantations of Ziziphus jujube.