A method for predicting the failure time and failure voltage of generator stator bars under the electrical stress test was proposed. The method established a general life prediction theory model for the electrical stress test based on the negative power-exponential model, and this model could predict the insulation life of stator bars under the electrical aging test and breakdown test. Then, we utilized Weibull distribution theory to estimate the life factor in the model and predict the failure time and failure voltage of the stator bars under the step-by-step test. The test results were consistent with the estimated results, and the correctness of the proposed method was verified.