Abstract: An important method to compute quasinormal modes of black holes is the WKB method. The main principle of this method is to match the two asymptotic solutions satisfying the boundary conditions with the approximate solution at the top of the effective potential across two turning points, so as to determine quasinormal modes. However, many literatures do not explain how the asymptotic solutions are matched. In this paper, a more reasonable explanation for this problem is given.

Key words: WKB method, quasinormal modes, asymptotic solution