A noncontact all-optical method for laser ultrasound detection is described.The surface acoustic waves(SAWs) were excited by employing a Nd:YAG laser on the sample Al plate with artificial surface-breaking defects and detected by a kind of optical difference detection system based on the optical beam deflection technique using a He-Ne laser.From the experiment,we attain the characteristics of reflected wave and transmitted wave generated by SAWs interacted with the surface-breaking defects,which show that the SAWs generated by laser line source are potential for the surface-breaking defects.