The mathematical simulations of the galvanic coupling intra-body communication (IBC) with different signal transmission paths have been introduced. Firstly, a galvanic coupling IBC circuit model was developed and the transfer function was derived. Secondly, the corresponding parameters were discussed. Finally, the signal attenuation characteristics of the galvanic coupling IBC were measured along the different signal transmission paths of the actual human bodies, while the corresponding mathematical simulations based on the proposed transfer function were carried out. A close agreement between the simulation results and measurement results has been demonstrated.