The human channel transmission characteristics of intra-body communication of implantable medical sensors are studied. A quasi-static field model of intra-body communication of implantable medical sensors is established using finite element method. An experiment platform was designed, which is used to verify the correctness of the model. The electrical potential gains are calculated as the intra-body electrical signal transmits along axial and radial directions when the model conductivity has isotropic and anisotropic characteristics, respectively. The results show that the intra-body communication signal attenuates obviously along the axial direction in the quasi-static frequency band, and the signal transmits stably along the radial direction. And the influence of frequency variation on signal gain is small; moreover, the signal gain for the anisotropic conductivity is obviously larger than that for the isotropic situation. The signal gains for intra-body communication and radio communication are compared, and the signal gain for intra-body communication is superior.