The embodiment of the invention discloses a water cooling structure for a high-power magnetic alloy cavity. The structure comprises a working tube, and a flange is arranged at one end of the working tube. A plurality of sheet-shaped annular magnetic alloy rings are fixedly mounted at the outer side of the working tube, and an annular groove shell is arranged at the outer side of the magnetic alloyrings. Guide plates which are fixedly mounted on the working tube and are matched with the magnetic alloy rings in shape are arranged at the two sides of the magnetic alloy rings. The annular grooveshell is fixedly connected with a guide plate, and the annular groove shell is communicated with a water inlet tube. The guide plate comprises a fixed plate and guide edges close to the magnetic alloyrings. Flow guide grooves are formed between the flow guide edges and is in a streamline shape which evenly divides the flow guide plates, wherein the ends, close to the water inlet tube, of the flowguide grooves are separated from one another, and the ends, away from the water inlet tube, are converged and make contact with the working tube of the annular groove shell. A water outlet groove isformed at the periphery of the working tube and is communicated with a water outlet tube. The structure solves the problem that in the prior art, due to the fact that cooling efficiency is insufficient, the magnetic ring is extruded by thermal stress and deforms, and the magnetic ring is damaged is solved.