Abstract: A lumped parameter method nodal model is developed for alkali metal cooled space reactor system dynamic characteristics analysis in this paper. The space reactor system dynamic response code was built by using Simulink, and the code was approved with steady state designed parameters. The transient response of space reactor was studied on the step responses of the increase in the drum angle and external load. The results show that the power increased rapidly, and then the power increased slowly to a final new steady state because of the core reactivity temperature feedback. When increased in external load, the TE electric power output increased rapidly and a great negative reactivity was brought to the core, thus the core underwent a rapid power decrease and core fuel temperature decreased. The TE electric power output responds to the change in external load in a much faster spend than the change in control angle.