Abstract: A laboratory soil incubation condition with moisture content 60% WHC and temperature at 25 ℃ was conducted to study dynamics of net mineralization,nitrification and acidification of four acidic agricultural soils with different initial pH,which were collected from a tea garden and three cropland in Yunnan province.The results showed that the mode of time courses for NH+4-N+NO-3-N accumulation followed a logistic model for soil II(pH 4.81,corn field) and Ⅳ(pH 6.02,vegetable field),exponential model for soil Ⅲ(pH 5.41,vegetable field).No significant mineralization was found for soil Ⅰ(pH 4.03,tea garden field).NO-3-N accumulation in the soil followed a first-order reaction model for soil Ⅱ,Ⅲ and Ⅳ without additional NH+4,and an addition of NH+4 stimulated the soil nitrification significantly.By inputting NH+4 ,initial pH of Ⅱ,Ⅲ and Ⅳ soil was significantly changed,resulting in a decrease in soil pH and an increase in soil exchangeable Al3+ content,which did not happen in soil I with or without NH+4-input.The results indicated that for some soil with a very low pH,such as pH 4.03,nitrification,pH and exchangeable Al3+ were not affected by the available NH+4.