An Ultra-Wide-Band(UWB) antenna with flexible material Polydimethylsiloxane(PDMS) as the dielectric substrate is designed. Its radiating element is composed of rectangular and semi-circular metal patches. The two-part structure is connected by a strip patch. The coplanar waveguide feeding method is adopted for the antenna. The above-mentioned metal patch is embedded inside the middle of the PDMS substrates; and this antenna can be used in a wearable system for human body communication. The embedded structure can effectively improve the flexibility and durability of the antenna. In order to better simulate the working environment of the antenna on human body, a three-layer human body tissue model including skin, fat and muscle is constructed. The maximum antenna specific absorption rate is 16.4mW that meets the international standards for human safety. Finally, the antenna samples are tested, and the results show that the overall performance of the antenna is stable, and the impedance bandwidth is 5.39-10.33 GHz, which meets the requirements of medical band(5.725-5.875 GHz).