Abstract: In order to clarify the microbial fertilizer’s contribution to soil fertility after being applied to soils with different pH values, the author studied bacterial microorganisms inoculated and cultured in sterilized soil and explored their survivability, law of change and contribution to the soil nutrient through plate colony counting method. The results showed that: the number of bacterial microorganisms rose rapidly in the first two weeks after inoculated into sterilized soil, and then entered into a relatively long period of stability. In neutral soil the abundance of various types of bacterial microorganisms were different. Ammonification bacteria were up to 108 cfu/g dry soil. Nitrogen-fixing microorganisms, bacillus bacteria, actinomycetes also reached 107 cfu/g dry soil, while mildew was at most about 105 cfu/g dry soil. When changed to acid soil with pH value around 4.5, the number of bacteria and actinomycetes reduced to only 1% of that in neutral soil. Maximum abundance of mildew could reach up to 107 cfu/g dry soil, while yeast quantity was only 1/10 of that of mildew. The rapid growth and reproduction of bacterial microorganisms could contribute to the increase of major nutrients and activity in the soils through its decomposition, nitrogen fixation and the solution of potassium and phosphorus.