Abstract: Traditional ways to evaluate the damage caused by thermal fatigue are almost destructive. According to the relationship between E and velocity of sound wave, a nondestructive testing method measuring velocity in different specimens of different thermal fatigue times was proposed. When Youngs modulus E and effective modulus of elasticity were got, then the damage parameter D was available, and hence ultrasonic testing of thermal fatigue damage could be achieved. Under this experimental condition, damage parameter D was increased to 0.1 after 300 times of thermal fatigue. The result showed that the aim of testing was realized.