The invention relates to a chloride-free potassium hydrogen sulfate preparation device. The device comprises a reaction tank, the reaction tank is divided into a first reaction zone, a second reactionzone and a third reaction zone, a retaining wall a is arranged between the first reaction zone and the second reaction zone, a retaining wall b is arranged between the second reaction zone and the third reaction zone, an overflow port is left above each of the retaining wall a and the retaining wall b, and an underflow channel is further arranged at the bottom part of the retaining wall b. The device is provided with the three-level reaction tank and double-layer stirring paddles, the reaction time of the material is guaranteed, the sufficient stirring of the material is guaranteed, the steamis introduced through multiple points, so that on one hand, the reaction heat is provided and the reaction time is maintained, and on the other hand, the solid liquid-gas interface is increased, anddevice is favorable for the overflowing of hydrogen chloride.