Abstract: Aging conditions of polyethylene (PE) pipes aged at 80℃ for different times (120, 240, 360 h) were analyzed by change of impact strength. The ultrasonic velocity spectrum and attenuation spectrum of different thermal aged samples were obtained by short-time Fourier transform (STFT), and then the relationship between the ultrasonic velocity, the attenuation coefficient and the impact strength was established. The relative impact strength of polyethylene was calculated to evaluate the aging degree. The results show that with the extension of thermal aging time, the impact strength, ultrasonic velocity and attenuation coefficient of polyethylene decreased. The relationship between impact strength and ultrasonic velocity, and between impact strength and attenuation coefficient satisfied a certain quadratic function. The relative errors between the impact strength calculated by the ultrasonic velocity or by the attenuation coefficient and the test result were both below 2%, indicating that the thermal aging degree of polyethylene can be non-destructively evaluated with ultrasonic parameters.