The method of images is an easy way to solve the problem of high symmetry electrostatic field boundary value problem. In this paper, the mirroring problem of the wedge boundary conductive system is studied, at this time there are additional conditions in the angle of the conductive wedge α=π/n（n=2,3,4,…）,   which is the question point of students in the teaching process. The theoretical basis for solving the electrostatic field by the method of images is the unique theorem, and under the principle of keeping the relationship between boundary condition and edge value unchanged, the mathematical expression of conductive wedge angle is deduced and the reasons for its additional conditions are explained.