This paper presents a trial solution for the predominant field distribution of an arbitrary order guided mode of Ti:LiNbO3 optical waveguides. The parameters of the solution can be reasonably determined by using the variational technique. And the propagation constant can be approximately obtained simultaneously. Compared with the extended effective index method and the effective index method, the main advantage besides its high accuracy and simplisity in methematical style is that the unknown parameters are easy to be determined. Also, we can obtain the analytical expression of the refractive index profile of the equivalent slab waveguide.