Abstract: The power transient model and reactivity feedback model on transient thermohydraulic characteristics analysis of Heat Pipe Segmeuted Thermoelectric Module Converters（HP-STMCs） cooled space reactorcore were built by using CFD interface UDF, and the HPSR core transient analysis code SNPS-FTASR was developed and approved with steady state calculation. The transient response of HP-STMCs core was studied on reactivity-insertion accident transient and a heat pipe failed transient. The results show that the power and UN temperature increased rapidly, then the power and temperature increased slowly to a final new steady state because of the core reactivity temperature feedback. The new power is 121.3% rated power. When a heat pipe failed, the UN fuel temperature increased rapidly and a great negative reactivity was brought to the core, thus the HP-STMCs core underwent a rapid power decrease and finally operated at 88.7% rated power. The maximum temperature of UN fuel increased by 140 K. It is approved by the result that the HP-STMCs core is safety at transient state including reactivity-insertion accident and a heat pipe failed.