Abstract: The physical mechanisms of ultrasonic generation by laser pulse, the waveform characteristics of the generated laser ultrasonic signal and the influence of laser parameters on the ultrasonic signal were analysed theoretically. And two experimental apparatus were built that received laser ultrasonic with a piezoelectric ultrasonic transducer or an optical detection method based on two-wave mixing interference to verify the theoretical analysis results. In the experiment, the influence of the pulse laser parameters and the characteristic of the detected signals with two different detection method were analysed. Through theoretical analysis and experimental verification, the generated ultrasonic amplitude can be affected by the incoming laser parameters, and optical detection method based on two-wave mixing interference can detect complete laser ultrasonic waveform information.