Phreatic surface is one of the most important factors to influence tailing dam security degree. Due to the extremely complicated seepage boundary conditions of tailing dam, the calculation results adopting two-dimensional simplified theory may be greatly different from the measured results. It is urgent need of an accurate calculation method to forecast phreatic surface. Based on analysis of affecting factors of phreatic surface in tailing dam, the phreatic surface SVM predicted method is bring forward to predict the phreatic surface. According to the daily observation of phreatic surface, the phreatic surface SVM predicted model obtained. Finally, a tailings dam projects is given to illustrate stability analysis method of tailings dam based on Phreatic predicted Method-based SVM.