Abstract: The control rod hydraulic driving line (CRHDL) is a new type of in-vessel control rod driving technology. The control rod hydraulic deceleration device (CRHDD) is one of the key components of the CRHDL. To prevent the control rod cross wing from being permanently deformed or damaged during the fast dropping rod process, the CRHDD performs the fast dropping rod deceleration function through the interworking of the slow-down plug and water filled cylinder. The hydraulic driving rod deceleration test was conducted to get the slow-down mechanism of the CRHDD, and a dynamic model was developed to analyze the key parameters of the decelerating process. The model calculation result agrees well with the experiment result, which verifies the accuracy of the model. Then the CRHDD performance calculation under reactor high temperature working condition was carried out through the CRHDD dynamic model. The above work lays solid foundation for the design and upgrade of the CRHDD.