In this paper, ultrasonic technology is proposed for the inner temperature of clutch case measurement of the slow response, inconvenient installation and large measurement error traditional temperature measurement. The in-depth study of the application of ultrasonic temperature measurement technology in clutch case has significant meanings to solve the problems in traditional temperature methods. Based on the finite element analysis software COMSOL, the physical model of ultrasonic wave propagation is established in the clutch case, and the temperature field of the clutch case is restored by the least square method, which can well solve the problem of complex coupling of physical field inside the clutch case. The results show that the internal temperature of clutch case can be obtained by ultrasonic measurement, and the maximum relative error between the calculation results of flight time and the theoretical results is 0. 26%; The results of temperature field reduction by least square method are consistent with the theoretical results.