Abstract: Abstract: In order to avoid excessive temperature rise which leads to permanent magnet demagnetization and damage of containment shell, the design of cooling circuit of magnetic pumps was discussed. Theory analysis showed that the cooling circuit had a great influence on magnetic pumps' efficiency and reliability. Analysis and calculation showed that the main heat source of magnetic pumps was the eddy current heat of containment shell. ANSYS-APDL was adopted to calculate the eddy current heat, which simplified the distribution of the magnetic field to two-dimensional. The total heat was obtained through the eddy current heat multiplied by an amplification coefficient k. The cooling flow rate was calculated according to the heat balance and the cooling circuit was designed. The flow field model of the cooling circuit was established by Pro/e software, the structured grid was adopted to mesh the model and the near wall boundary layer was refined to ensure the grid quality. The SIMPLEC algorithm and the k-ε turbulence model were adopted to solve the N-S equations and energy equation by CFX code. The flow velocity, pressure and temperature distribution were obtained by CFX software post. As could be seen from the numerical simulation, the internal flow of the cooling circuit was spiral motion combining circular motion and linear motion. Through the comparison between internal and external cooling circulations with the same main geometric parameters, it showed that the temperature rise was the highest, and the pressure was low in the internal circulation located in the bottom of containment shell, which maybe caused cavitation. On the other hand, the temperature distribution was uniform and the pressure gradually reduced from shaft hole to external pipeline (the pressure of containment shell bottom was higher) in external cooling circulation, which met the design requirements. Based on the same cooling flow rate, the influence of the shaft bore diameter in external cooling circulation was analyzed. It showed that the spiral movement velocity of cooling circuit was mainly decided by the circular velocity, the axial velocity had a little effect on the system, and a certain level of fluctuations of shaft bore diameter designed had little influence on the cooling result when the cooling flow rate was fixed. Without considering the friction changes at different rotational speeds, the influence of rotational speed was also discussed in external cooling circulation. It showed that the rotational speed powerfully affected the heat transfer. The highest temperature reached 386 K when the internal magnetic rotor didn't rotate, which was far exceeding the safety range, but the highest temperature was basically stabilized at a reasonable range with the internal magnetic rotating. The wall heat transfer coefficient increased significantly with the increase of rotational speed. So the increase of pump's rotational speed can promote heat exchange between the different fluid layers and improve the cooling effect. The research is helpful for the design of cooling circuit in magnetic pumps.