Abstract: In this study,the effect of pH and nitrate thorium concentration on the precipitation ratio of thorium was investigated.Also,the effect of temperature,precipitator adding velocity and ageing on the form of precipitate was studied.The result shows that the precipitation ratio increased with the increasing of pH value on the condition of pH＜5.3;when the pH＞5.3,the precipitation ratio decreased with the increasing of pH value,and the precipitation return to dissolve evidently when the pH＞7.The form of thorium precipitate is amorphous.Adjusting the reaction temperature,the velocity of adding precipitate and the time of ageing could not make the amorphous precipitate transform into crystal precipitate.