In recent years, effective methods for predicting and suppressing EMI over a broad band are required. In this paper, we focus on an equivalent circuit model for predicting EM radiation from a surface-microstrip line (S-MSL) structure with an interconnection coaxial cable. Firstly, frequency responses of common-mode (CM) current on the interconnection coaxial cable and EM radiation are studied experimentally and compared with FDTD modeling. It was demonstrated that the ground plane of the interconnected PCBs and the interconnection cable are the dominant radiation factor at low frequencies. Secondly, an equivalent circuit model for predicting CM current in the ground-connection model was proposed. The equivalent circuit model is based on consideration of concepts of CM antenna impedance to current- and voltage-driven mechanisms. Its validity was discussed by comparing FDTD simulation results. The good agreement between the predicted and measured results indicates the validity of the equivalent circuit model.