Abstract: Based on the sub-cell Finite-Difference Time-Domain (FDTD) method, an equivalent field-to-line coupling numerical model for transmission line common-mode electromagnetic leakage is provided to calculate the inductive coupling and capacitive coupling between parallel transmission lines. The new model can solve the coupling crosstalk problem under inhomogeneous media and other complex situations. In addition, the presented work describes such method for numerical calculation, which has a more concise form. With the new model, simulation of common-mode electromagnetic information leakage for parallel transmission line is implemented. Furthermore, both simulation in time domain and experimental results in frequency domain show that the numerical model can effectively describe the emission characteristics of common-mode electromagnetic information leakage for parallel transmission lines.