Abstract: The 10 MW High Temperature Gas-cooled Reactor-Test Module (HTR-10) is the first module high temperature gas-cooled reactor in China. The helium circulator trip test is one of the commissioning tests conducted on the HTR-10. This test not only verifies the safety features of the HTR-10 after the loss of forced cooling condition, but also provides the measured data for the validation of system analysis codes. Based on the actual test conditions, the helium circulator trip test was simulated using the THERMIX code. Furthermore, main reactor parameters of interest were analyzed. The calculated reactor power agrees well with the test one, thus the validity, reasonability and applicability of THERMIX are fully demonstrated. During the test process, the maximum fuel center temperature is always below its limit value of 1 230 ℃.