Home health care system and long term physiologic parameters monitoring system are important for elevating the living quality of chronic disease patients and elderly. Elaborating towards a sophisticated and comprehensive home health care system, Intra-Body Communication (IBC) is believed to have advantages in power consumption, electromagnetic radiation, interference from external electromagnetic noise, security, and restriction in spectrum resource. In this article, we start from quasi-static Maxwell's Equation and propose a mathematical model, which includes electrical properties and proportion of human tissues, for IBC on a human limb. By solving the mathematical model analytically and conducting in-vivo experiment, our model has shown adequate agreement with experiments.