A strain of Thiobacillus ferrooxidans was isolated from underground acid water in a mine by alternate culture with liquid and solid culture mediums.The influence of different initial Fe2 concentration on oxidation activity of Thiobacillus ferrooxidans,as well as the influence of initial Fe2 concentration and pH value on precipitation in the process of culturing was studied.The results show that the best condition for decreasing precipitation and improving oxidation activity of the strain of Thiobacillus ferrooxidans is initial pH value 2.0,initial Fe2 concentrate about 9.05 g/L.