Intra-body communication (IBC) utilizes the human body as the data channel to ensure the signal transmits through the on-body and implanted sensors. It offers a low power, low radiation and high transmission quality method for currently fast developing Body Area Network (BAN). In our previous work, the theory model and simulation of the physical model have been researched. In order to design and implement the IBC system, the channel model should be investigated. In this paper, a channel model of the IBC was constituted, including the signal generator, modulator-demodulator, human channel with AWGN noise and equalizer module. Then, in order to attain the attenuation properties of the human channel, the in vivo experiments with 7 volunteers were carried out through the signal analyzer with trace generator and the differential probe. Due to the frequency-dependence of human channel attenuation, the equalizer was designed to compensate frequency distortion. The effect of the equalizer was approximated to the amplifier, filter and reshape in the communication system. At last the constellations diagrams of PSK, BER versus SNR of intra-body communication system were investigated. The results showed that the human body has a stable propagation characteristic in the frequency range from 10 kHz to 500 kHz with different volunteers. The constellation diagrams with the equalizer were much better than the situations without the equalizer. It indicated that the ISI (inter-symbol interference) induced by the frequency distortion of human channel was effectively reduced by the equalizer. FSK can achieve the lowest BER versus SNR and it was the best modulation for communication system. QPSK and BPSK had the similar BER with SNR. Yet the 8PSK was the worst collection.