ABSTRACTIn this paper, the electromagnetic propagation of a Gaussian beam with oblique incidence is analyzed in an inhomogeneous stratified medium. The transmission and reflection coefficients of a finite inhomogeneous layer are calculated for a perpendicular polarization using the spectral parameter power series method; these coefficients are implicit in the asymptotic formulas obtained for the electric field, the complex stationary-phase method is applied to solve them. The results obtained of reflectance and transmittance by the SPPS method are compared against the results obtained by the DTMM and WKB methods, and it is calculated the absolute error respect to exact solutions, besides other numerical results are obtained.