A structure of extrinsic optical fiber F-P sensor is designed.The mathematic optimal model of dual wavelength optical fiber F-P sensing system is established.The length of F-P cavity and wavelengths of two output light are designed by adopting optimum method.The experimental device of laser ultrasound based on optical fiber F-P sensing system is established.The relations between parameters of laser and sample and ultrasonic waveform’s characteristics are studied.The experimental results show the sensing system can detect laser ultrasonic wave signal efficiently.Its operation is simple.It is low cost and easy to realize.The characteristics of ultrasound waveform depends on the parameters of laser and sample mostly.