3 m high temperature wind tunnel of China Aerodynamics Research and Development Center is a 3-meter-scale free-jet wind tunnel built recently in China, which is used to conduct aero-thermal loads, aero-thermo-structures, high-enthalpy aerodynamics research and air-breathing propulsion systems testing at different total enthalpy conditions which are conformed to the realistic flight environment. The high-enthalpy flow is produced by burning isobutene, liquid oxygen and air in the combustor, and then goes through the expansion section of nozzle, passes the test section in which the flow is uniform. In the downstream of test section, the flow is exhausted by the diffuser and then arrives at vacuum tank. In order to evaluate the wind tunnel performance, a series of flow field calibration tests were conducted within Mach numbers 4～7. The results indicate that the diameter of uniform flow area is more than 80% of nozzle outlet diameter. In the test section in which the flow is uniform , the deviation of the Mach number and total temperature of flow are within two percent of the average Mach number and total temperature respectively. The tunnel has the ability to simulate Mach number, dynamic pressure, total enthalpy, oxygen components and flight time at Mach numbers of 4～7 and altitudes of 17～30 kilometers. The highest total temperature of flow is 2335 K. The flow field is very stable during long-time operation. The maximum fluctuation of Mach number and total temperature is no more than 2%. The HHT will carry out aerodynamic, propulsion, materials and structures evaluation tests of hypersonic aircraft in the future.