Abstract: After the improvement of the temperature resistance level of the control rod drive mechanism (CRDM) of the reactor, in order to analyze whether it is feasible to eliminate the forced ventilation system of CRDM, a calculation model of the airflow field intended for single CRDM is established to determine the calculation method and boundary condition, which is conducted by fitting with the experiment results. The temperature field and the airflow field of the full-scale CRDM clusters are calculated, and the temperature field effect of the full-scale CRDM clusters is obtained based on the natural flow field. The research results reveal that the natural convection could take the heat generated by the CRDM clusters out of the reactor pit without pit fever effect. Moreover, as the CRDM clusters output power increases, the natural circulation intensity increases as well. The natural convection could cool down the CRDM coils. Thus, the forced ventilation system could be eliminated with the improvement of the CRDM temperature resistance level.