In this paper we present an essentially analytic method for solving multilayer metallic optical waveguides using the asymptotic theory. The wave number is expanded into asymptotic series in terms of a small parameter. This method is exact and can approach any accuracy desired. However, the numerical results for four layer and five layer structures show that the second order solution is accurate enough. It is simple and has the same form of expressions for TE and TM mdes and different layer structures.