Abstract: Both the primary helium circulator for high-temperature gas-cooled reactor (HTR) and the primary pump for the pressurized-water reactor are the key components in the reactor primary loop. Under the normal operation, their function requirements are the same, but under the accidental operation, their functions are different from each other due to the different behaviors of the reactor. The stopping behavior of the primary pump has been studied in the experiments and the reactor plant, however, the study on the stopping behavior of the primary helium circulator for HTR is very lack. In this study, the stopping behavior of the primary helium circulator was studied theoretically with considering the effects of resistance characteristic of the primary loop and the aerodynamic of the helium circulator itself. The equation for the prediction of the flow rate and the rotating speed at the stopping period were deduced. The numerical simulation result was given for the safety analysis in the preliminary design of HTR.