By use of the hardware of MIA-3 autoanalytical system, we developed a special software according to the need of research, and set up an autotitration system which can be used in constant pH, and tried to apply it to the telease process of surface hydroxyl of a latosol with great iron oxidex.The results conform that the quantities of hydroxyl released are affected by pH and the amount of SO₄^2- added in Na₂SO₄ solution, and that the dynamic changes of hydroxyl release accord with Elovich equations.