[en] The step dynamic process of the hydraulic control rod (HCR) has been achieved by experiments. This paper reveals the action mechanism of the HCR, gives detailed analyses of the relationship among the dynamic feature, the control rod and combined valve performance parameters, and the combined valve operation. The results indicate that the step process of the control rod is affected by the output flow pulse of the combined valve, pressure wave, and heavily damped pressure oscillation that is produced by the step cylinder movement. The performance parameters of the step cylinder limit the flow range in its stationary balanced state and also limit the capability of absorbing the flow pulse and pressure wave in its step process. The performance parameters of the combined valve determine the quantitative values of stationary balance, delay balance, flow pulse and pressure wave. The relation of both parameters determines the step state of the control rod. (author)