Abstract: The extent of the thickness uniformity of the thermal protection layer of the solid rocket motor will affect the working performance of the engine. To measure the thickness of the thermal protection layer, a thermal protection layer thickness detection scheme based on laser ultrasonic is designed. By analyzing the characteristics of laser ultrasonic thickness measurement of thermal protection layer, the echo signal which was collected is denoised by wavelet transform, and the positional feature information of the two interfaces is effectively extracted by wavelet transform modulus maximum method, and hence non-contact measurement of the thickness of the thermal protection layer is realized. The experimental results show that the relative error measured by this method is within 6.4%.