Intra-body communication (IBC) is a novel short-range non-RF(radio frequency) wire-less communication technique specified by the IEEE 802.15.6 using the human body as a transmis-sion medium. In this work, a new modeling method of the IBC system based on the composite fad-ing channel is proposed, where the cascaded filter is used to express the composite fading channel and the modulation method in transmitter and receiver. The composite fading channel combines with the average attenuation, group delay, multipath effect, and shadowing effect. The modulation is adopted orthogonal frequency division multiplexing (OFDM), and thereby the constellation, cyc-lic prefix, bit error rate, and pilot mode are determined. As a result, the whole process and multi-parameter simulation of IBC system can be achieved. It provides a theoretical foundation for the system design of the intra-body communication and will promote its application to the wireless body area network (WBAN).