Two tests initiated by unscrammed control rod withdrawal were performed on the High Temperature Gas-Cooled Reactor-Test Module (HTR-10) in November 2003 after the reactor achieved its full power, and the test con-ditions represented a typical transient scenario of modular high-temperature reactors (HTRs), called pressurized loss of forced cooling, and anticipated transient without scram. Based on the test parameters, the HTR-10 thermal behav-iors under the test conditions were studied with the help of the system analysis code THERMIX. The combination of the test results and the investigation results makes the HTR-10 safety potential better understood. Key phenom-ena, such as the helium natural circulation and the tem-perature redistribution in the reactor, were revealed. As the safety feature of most significance, there is a large margin between the maximum fuel temperature and its safety limit in each test. Temperatures of thermocouples in different components were calculated by THERMIX and compared with the test values. The applicability of the code was verified by good agreement obtained from the comparison.