The ultrasonic time-of-flight-diffraction (TOFD) detection method has been widely used in crack size assessment. The key issue in TOFD is to determine the arrival time of crack tip diffracted signal. In the traditional cross correlation method, the resulting maximum peak of cross correlation function between two signals indicates the time of flight between them. In practical ultrasonic measurement, the transmission wave may be distorted and phase shift may be introduced. This paper presents a method using cross correlation and phase shift correction to improve the accuracy of crack sizing in the TOFD framework. The resulting maximum peak of the cross correlation function between two signals combining with time delay introduced by phase shift determine the arrival time of diffracted signal. Experimental results are used to demonstrate the advantage of the proposed method.