Abstract: The compact integral effects test (CIET) facility was designed to investigate the thermal hydraulic responses of fluoride-salt-cooled high-temperature reactor. CIET facility uses DOWTHERM A fluid to simulate fluoride salt. Thermo-physical properties and transport of DOWTHERM A were implemented into the RELAP5/MOD3.2. The modified RELAP5 code was adopted to study thermal hydraulic behavior of DOWTHERM A under forced circulation operation and natural circulation operation of CIET facility respective-ely. Calculation results of core inlet and outlet temperatures and the coiled tube air heater outlet temperature are in good agreement with the corresponding experimental data under forced circulation operation. The inlet temperatures of coiled tube air heater are slightly different from the experiment data. In natural circulation the computational results indicate that the decay heat is mainly removed through the DRACS. The computational flow rates of DHX and DRACS are close to the experiment data. Furthermore, the relative error of flow rate between calculation results and experiment data is about 10%. The results prove the accuracy of the modified RELAP5/MOD3.2.