The invention relates to a manufacturing method of a horn antenna, in particular to a manufacturing method of a millimeter wave horn antenna based on an MEMS (Micro-electromechanical Systems) process. The method comprises the following steps: selecting a substrate, cleaning the substrate, coating a photosensitive adhesive in a spinning way, and performing ultraviolet lithography to obtain a die of a horn antenna array; covering the die with a layer of curable flexible material, and removing the die after the flexible material is cured to obtain the main body of the horn antenna array; coating the front side of the main body with a layer of photoresist in a spinning way, performing lithography development on the photoresist, leaving the position of a horn cavity in the front side of the main body, and metallizing the position; stripping a sacrificial layer to obtain a metalized horn antenna array model; making a feeder line on the back side of the horn antenna array model to obtain the horn antenna array. In the process flow, smaller sizes can be realized on the basis of the MEMS process. Compared with an antenna array with a micro-strip line structure, the horn type antenna array has the advantages that higher radiation performance is realized, and lobes in a main plane can be separately controlled more easily.