Abstract: This paper studies the termination responses of a shielded cable within a cavity with slot under external electromagnetic field, using a mixed method combining the finite difference time domain(FDTD)method with the transmission line model of the shielded cable. The excitation fields of the cable are computed firstly with the FDTD method, and then the responses of the terminations are computed using the transmission line model. The mixed method requires small memory and computation quantity with ease of use. The study shows that the shield of the cable has good shielding capabilities for external electromagnetic interference.