The computing formula of the electric field strength transmission coefficient of p polarized light in layered media is obtained by theoretical computation, and verified by finite difference time domain(FDTD) method. This formula is similar with that of the traditional transmission coefficient of p polarized light in layered media computed by characteristic matrix method. The difference is that when the total internal reflection (TIR) occurs, a TIR correction factor arises. Furthermore, a two layer TIR structure and a surface plasmon resonance (SPR) film structure are simulated by FDTD method, and the results are in good agreement with those of the correction formula. This correction formula is a perfection to the propagation of electromagnetic wave in layered media, and an amendment to some influential references about the description of the field enhancement factor. It also has reference value for the researches on SPR and the evanescent field.