With　the　development　of　microelectronics　and　sensor　technologies,　implantable　electronic　devices　are　employed　in　many　applications.　These　devices　are　distributed　on　or　in　the　human　bodies　and　are　used　to　transmit　signals　wirelessly　to　external　equipment.　In　conventional　wireless　communications,　the　antennas　need　a　lot　of　space　and　power,　and　their　strong　electromagnetic　interference　limits　the　available　locations　for　implantable　devices.　In　the　more　recently　developed　galvanic　coupling　intra-body　communication　technology,　human　tissues　are　used　as　the　media　of　signal　transmission,　and　this　method　has　therefore　been　applied　to　resolve　the　spatial　limitations　of　conventional　wireless　communications　methods.　This　paper　presents　a　mathematical　model　of　multi-layer　galvanic　coupling　based　on　the　volume　conductor　theory　to　analyze　the　transmission　mechanism　of　these　implantable　intra-body　communication　devices.　The　proposed　model　is　based　on　the　quasi-static　approximation　conditions　of　Maxwell＇s　equations,　the　field　and　potential　are　solved　from　Poisson＇s　equation,　and　an　equation　was　obtained　to　model　the　channel　attenuation.　The　channel　gain　in　a　model　of　human　limbs　can　be　used　to　calculate　within　the　frequency　range　of　lesser　than　1　MHz.　To　verify　the　accuracy　and　applicability　of　the　model,　the　computed　results　were　compared　with　the　physiological　saline　and　porcine　tissue　experimental　results　in　the　100-kHz　frequency.