An extended Wheeler's conforming mapping method is proposed to analyze the characteristic parameters of the multilayer based on the simple Wheeler's transformation. The explicit expression between the microwave characteristic parameter and the each layer parameter is obtained. Compared with the results obtained by the quasi-static finite element method (QS-FEM), our results show that the present approach can not only accurately evaluate the characteristic parameters of the multilayer but also have a great computational efficiency. Based on this method, a modified structure of the typical electro-optic modulator is given. The velocity matching and the impedance matching can be achieved simultaneously by adding a compensation layer.