An air-heater was designed for scramjet ground test. The internal flow field in the air-heater was investigated and the results were compared with the test data. The results show that the air-heater basically corresponds with the structure project and performance, the temperature of faceplate is reduced as a result of the air flow from injector-inlet, and the inner surface of the combustion chamber is protected by air flow from chamber-inlet. The results will be helpful for the optimization of the air-heater design.