In the electrical test and operation of generator, the hypotenuse electric field at the end of stator winding is very high, which is a weak part that corona discharge often occurs. In this study, an analytical model and a finite element model of the hypotenuse electric field at the end of stator winding were established. The influencing factors and laws of the hypotenuse electric field were studied, and the influence of the hypotenuse clearance, rotating angle, and dielectric constant of the filling medium on the maximum electric field was analyzed. An effective method to optimize the electric field at the end was presented. The results show that under the in-phase winding, the hypotenuse electric field can be optimized by decreasing the surface electric field of stator bar, the width of bar, and the rotating angle of bar or increasing the hypotenuse clearance; Under the out-of-phase winding, the hypotenuse electric field can be optimized by increasing the dielectric constant of filling medium and the hypotenuse clearance of winding. The finite element model of hypotenuse electric field can accurately analyze the maximum electric field and the distribution trend at the end of winding. The correctness of the model is verified by corona test of UV imaging equipment, which indicate that that the model has good engineering application value.