In order to meet the high-speed working requirements of the fifth-generation mobile communication, a high gain antenna for 5G millimeter wave based on SIW is proposed. Through the coupling between the rectangular patch and the resonant cavity, and arranging parasitic units on both sides of the main unit, the working bandwidth of the antenna (S₁₁≤−10 dB) reaches 10.7% (3.36~3.74 GHz) . The maximum gain in the working range reaches 7.78 dBi. Compared with other similar antenna, the proposed antenna can reduce 2/3 of the phase shifter and it uses Fr-4 material,which is of greater cost advantage.