The invention belongs to the technical field of slot array antennas, and provides a millimeter wave high gain slot array antenna based on a MEMS process, which is used to solve the problem that the antenna gain can be further improved under the condition of limiting the antenna area or the fixed beam width. The millimeter wave high gain slot array antenna utilizes the MEMS process, and in order tofacilitate the shaping of the pattern, a gap is used as an antenna radiating element. In order to meet the fixed antenna beam width requirement and simultaneously increase the antenna gain, a radiation matching layer and a radiation surface layer are loaded above a conventional radiation slot unit, the sizes of the air cavities of the radiation matching layer and the radiation surface layer and the radiation slit position are properly adjusted, and therefore, the effect for improving the antenna gain in the condition of not changing the wave beam width is achieved.