Abstract: When measuring the cladding thickness of rocket motor by ultrasonic means, the obtained echoes of the thin cladding will overlap in the time field. Based on the characteristics of overlapped echoes, a new method for time delay estimation was presented. The method consisted in taking the envelope of the inverse Fourier transform of a corrected measured signal. Experimental results showed the method could estimate the delay time of the overlapped signals accurately. It improved the measuring precision of the thickness of rocket motor cladding.