This study analyzed the signal loss characteristics of non-resonant and resonant couplings to determine the optimum design of magnetic coupling intra-body communication. Magnetic coupling intra-body communication typically uses coils as transmitting and receiving antennas. Non-resonant coupling is a method that arranges one coil on the transmitting and receiving sides, respectively, and transmits the signal through pure magnetic coupling between the coils. On the other hand, resonant coupling is a method that introduces coils and capacitors for resonance in addition to the transmitting and receiving coils, and attempts to reduce the signal loss by utilizing resonant phenomena. This study developed the equivalent circuits on each coupling to calculate the frequency characteristics of both non-resonant and resonant coupling using computer simulation. The frequency range calculated was 100 kHz to 10 MHz and the resonant frequency was 2 MHz. For non-resonant coupling, this study revealed that the frequency at which the signal loss was minimal was determined by the self-inductance of the transmitting and receiving coils. Furthermore, the resonant frequency characteristics could be fundamentally controlled by the load resistance as well as the coupling coefficient between the resonant coil and the transmitting (or receiving) coil.