Abstract: The welding temperature during the linear friction welding is the key parameter to study the formation and change mechanism of joint microstructure. According to the characteristics that the temperature field of weldment (excluding flash) remains basically unchanged in the quasi stable friction stage of linear friction welding process, and the heat generated is mainly taken away by flash. The average temperature of welding interface of titanium alloy TC17 in quasi stable friction stage during friction welding is solved through theoretical analysis. The temperature changes at different positions of the welding interface during linear friction welding of TC17 titanium alloy were measured by semi natural thermocouple. The results show that the measured temperature of the welding interface at the quasi stable friction stage of TC17 under typical parameters is about 1 228 ℃, and the cooling speed to 500 ℃ after welding is about 52 ℃/s. In the quasi stable friction stage, the temperature difference between the center point and the edge point of the welding interface is no more than 10 ℃, and the heating rate and cooling rate of the center point of the interface are higher than those of the edge point. The difference between the measured value and the theoretical calculated value is not more than 10%.