In view of the difficulty of accurately characterizing the temperature field distribution of the rotating centrifugal water cooling of the highpower permanent magnet coupling with the traditional runner static or rotating speed substituted into the empirical formula to calculate the heat dissipation coefficient, the method of fluidstructure coupling heat transfer combined with the MRF model was proposed, and the 800 kW permanent magnet coupling was taken as example, the simulation calculation and heat dissipation optimization were carried out to obtain the flow field distribution of the runner and the temperature distribution of the whole machine. The conclusionsare as follows: the cooling water flow rate accelerates with the centrifugal action, and the speed decreases to 67 m/s after the energy loss at the outlet rightangle bend; under the heat loss 60 kW, the temperature distribution gradually increases along the radial direction, the highest temperature is 131 ℃, and the lowest is 76 ℃; comparing the influence of different heat loss and the number of runners on temperature, resistance torque, magnetic flux coefficient and other parameters, it is known that 40 is optimal number of runners, and the temperature is lowered by 6~8 ℃ compared with the original model with 36 runners.