A high-gain antenna with multi-layer phase-gradient metasurface (PGMS) lens is proposed. It consists of three parts, feed antenna, PGMS lens and back cavity. The proposed PGMS can transform quasi-spherical electromagnetic wave to plane wave within the frequency band 5.5-6.5 GHz. The half-power beamwidth of the feed antenna is reduced by up to 83.1 , and the gain is increased by up to 8.7 dB. Because the loading of the lens increases the back lobe, this article also introduces an antenna back cavity, which reflects the energy radiated from the antenna back to the front, thereby improving the radiation performance of the feed antenna. The measured results are in good agreement with the simulation results, verifying that the loading of the lens and the back cavity can achieve the purpose of increasing the gain and reducing the back lobe. The cavity-backed lens antenna provides potential application for microwave imaging and wireless communication.