Abstract: The safety rod system is the actuator for reactivity control and nuclear safety protection in Topaz type space nuclear reactors. Due to the uneven distribution of reactor core temperature field during the operation of a Topaz type space nuclear reactor in outer space orbit, the thermal expansion of the safety rod guide tube inside the nuclear reactor will cause certain radial deformation. When needs to stop the reactivity of nuclear reactor, the safety rod is affected by frictional resistance caused by collision with the bent guide tube during the emergency reset process. In the rod drop study for pressurized water reactor (PWR) control rods, the guide tubes are bent radially due to seismic and thermal loads, and even the shape of guide tube become “C” or “S” under different loads. How different shapes of guide tubes affect control rod drop is a variable studied by many researchers. In space nuclear reactors, only the effect of heat load on the guide tube needs to be considered, and the safety rod cannot rely on gravity, but is ejected into the reactor through the drive mechanism. In this paper, the changes in rod drop time and frictional resistance when the radial deformation of the guide tube exceeds its minimum clearance with the safety rod were researched. The radial deformation of the guide tube caused by the temperature field calculation results was taken as the input variable of the simulation analysis. A dynamic model of the safety rod system was established based on three-dimensional multi body dynamics simulation software. By accurately simulating the friction collision process and reasonably handling the rigid flexible coupling problem, the influence of radial deformation of the guide tube on the emergency reset of the safety rod was calculated and analyzed. It can be found that when the radial deformation of the guide tube exceeds 0.16 mm, the parameter sensitivity of the studied variable increases. At the same time, the variation of friction value is more complex and the contact collision is more violent. Through the simulation analysis, the maximum bending deformation of the guide tube is determined, and the failure of the safety rod to achieve the design goal due to excessive deformation is avoided. The simulation results show that the radial deformation of guide tube is positively correlated with the rod drop time and friction resistance of safety rod, which can provide reference for the design of safety rod system.