Laser-induced ultrasonic technology has been extensively studied and widely applied recently, for its advantages such as noncontract operation, nondestructive testing, broad bandwidth, high time, and space resolution, no shape limits on samples, etc. Firstly, the principles of laser ultrasonic generation and detection were introduced. Secondly, the application of the ultrasonic ratio method in measuring the surface defects was presented in detail. The experimental results were analyzed. Because the ratio method avoids measuring the velocity of the surface wave and reduces the experimental error, it is much more practical, reliable and effective in surface defect measurements.