Creeping wave theory is re-visited for BAN (Body Area Network) channel modeling. The formulation takes the characteristics of both antenna and human tissues into account. The field density at a certain distance from the radiating antenna can be directly determined by input power and on-body antenna gain. It is observed that the complicated on-body antenna gain measurement can be replaced by measuring antenna gain above infinitely large PEC (perfect electric conductor) plane to determine field density. Using time gating technique, the antenna gain above infinitely large PEC can be obtained by measuring continuous field on finitely large PEC, which is much easier to use in practice. The whole concept is validated through CST Microwave Studio. A very good agreement between the analytical model and full-wave simulation results is achieved.