Abstract: Depending on the present researches and the trend of future body area network (BAN), this paper investigates the electromagnetic channel characteristics for human arm. Two same all-fabric patch antennas, working at 5.8 GHz and with the size of 4 cm×4 cm, are taken as the transmitted and received antennas to study the transmission characteristics in the upright situation. And three classic positions are chosen to mimic the activity of arm in the process of natural walk, they are the maximum position of front swing, natural sagging, and maximum for the back swing. From the comparisons of different positions between the measured results in the air and those of on arm, the influence of surface wave is determined, and its predictive model is derived for the relative path loss by means of mathematical fitting method. The corresponding path loss models are also built for the above natural positions. The results show that the simple minor corrections for the path loss model of natural sagging can be used to predict the channel characteristics for the other two situations.