In this paper, a broadband, low RCS antenna based on polarization conversion metasurface (PCM) is designed and simulated. The metasurface unit, consists of a quasi-square patch on the top layer, a notched square ring on the mid layer and a metal ground, can realize cross polarization conversion within 5.87-20.67 GHz (111.5%). By arranging each unit properly, proposed metasurface achieves RCS reduction in the range of 8.21-21.22 GHz (88.41%). Rather than simply being loaded on the top of the antenna, the PCM functions as a part of radiators, which makes it possible to broad the bandwidth and enhance the gain simultaneously. Finally, a broadband antenna operating in the X-band is achieved, with a bandwidth of 7.76-12.59 GHz (47.5%).