The invention discloses a production method of monopotassium phosphate. A production device comprises a feed calcium slurry tank (1), a reaction tank (2), a feed calcium slurry pump (3), a reaction slurry pump (4), a first automatic back washing surface filter (5), a primary evaporator (6), an impurity removal and desulfurization tank (7), a second automatic back washing surface filter (8), a slurry pump (9), a secondary evaporator (10), a mother solution pump (11), a crystallizer (12), a crystal mush pump (13), a flat plate scraper centrifuge (14), a drier (15), a methanol delivery pump (16), a methanol recovery storage tank (17) and a methanol condenser (18). With the adoption of the production device and a production technology flow, feed calcium hydrophosphate and potassium hydrogen sulfate generate replacement reaction, so that the content of a produced product can reach 98%, the cost is greatly lower than the production cost of a product obtained by a neutralization method production technology, and the production method is simple in technology and extensive in raw material source, and has broad market application prospects.