Abstract: China Advanced Research Reactor (CARR) control rods are driven by the magnetic force produced by electrical coils. An out of pile testing loop was specially constructed to simulate CARR thermal-hydraulic conditions for the test. Some problems were found during the experiment, and several proposals of improvement were offered for the modification of the driving mechanism and accepted by the CARR engineering department and the designer. The modification to the driving mechanism was implemented, and the important parameters were measured, such as the balance temperature of the coils, the rod drop time, the coolant flow limit, and the load limit. The results show that the modified control rod driving mechanism meets design requirements.