Abstract: Control rod hydraulic drive system (CRHDS), which is invented by Tsinghua University for the nuclear heating reactor, is a new type of internal control rod drive technology. Control rod hydraulic deceleration device (CRHDD) is one of the major components of the CRHDS. The CRHDD performs the rod drop deceleration function to reduce the peak impact force acting upon the control rod under the premise of meeting the full length scram time criterion. The composition and working principle of CRHDD were analyzed. The different schemes of the hydraulic deceleration cylinder side wall flow channels were specified and tested by the CRHDS scram performance experiments under room temperature. The rod drop deceleration working mechanisms of different side wall flow channel schemes were compared and analyzed based on the experimental results, and the change rules of the characteristic parameters of the rod drop process with different side wall flow channel schemes were obtained and analyzed. The analysis results show that with the increase of the flow hole area of the side wall flow channel, the scram time decreases, and the peak rod drop velocity increases. When the flow hole area is above 0.004 m2, with the increase of side wall flow hole area, the peak rod drop velocity increases very slowly, the steady velocity of the rod drop process and the rod drop delay time change slightly, and the velocity increases slowly when the rod hits the bottom plate spring. The experimental research results lay the base for theoretical model build-up for the CRHDS scram process and can give guidance for the design and optimization of the CRHDD.