Abstract: A kind of spherical water-cooled calorimeter including the ball crown calorific body and the heat shield is developed. The fluid-thermal coupling model of the calorific body and test water is established. The water temperature distribution characteristics in the waterway and the influence of water temperature on the heat flux measurement result are analyzed based on the model and heat flux calibration test. The results show that the closer the water in the waterway is to the heated surface, the higher the water temperature is and the greater the radial temperature gradient is. The smaller the water mass flow rate is, the greater the radial and axial temperature gradients are. So the thermocouple should be kept away from the heated surface and closer to the central axis of the waterway when the water-cooled calorimeter is designed. And the water-cooled calorimeter should be calibrated and the appropriate water mass flow rate range needs to be determined before use. Finally, the test results show that the spherical water-cooled calorimeter can be used to measure the stagnation point heat flux accurately in the long-term arc-heated wind tunnel test with multiple heat flux states.