Ultrasonic is one of the most common uses of non-destructive evaluation technique. It could detect flaws inside the structure and on the surface such as voids, holes and cracks. In this investigation, a 304 steel block with a surface-breaking crack was fabricated. A series of test specimen with different depths of surface-breaking crack ranging from 2mm to 9mm was fabricated. The depth of the surface crack was evaluated by the pulse-echo ultrasonic technique. In this work, 2.25MHz, 5MHz and 10MHz of incident waves were employed to detect the depth of the surface-breaking crack. The effect of incident angle on the measuring accuracy was investigated. Experimental results showed that the accuracy of crack sizing detection by ultrasonic technique is not only dependent on the frequency of the incident wave but also dependent on the incident angle.