An ultrasonic sensitivity-improved fiber-optic Fabry-Perot interferometer(FPI)is proposed and employed for ultra-sonic imaging of seismic physical models(SPMs).The FPI comprises a flexible ultra-thin gold film and the end face of a graded-index multimode fiber(MMF),both of which are enclosed in a ceramic tube.The MMF in a specified length can collimate the diverged light beam and compensate for the light loss inside the air cavity,leading to an increased spectral fringe visibility and thus a steeper spectral slope.By using the spectral sideband filtering technique,the collimated FPI shows an improved ultrasonic response.Moreover,two-dimensional images of two SPMs are achieved in air by recon-structing the pulse-echo signals through using the time-of-flight approach.The proposed sensor with easy fabrication and compact size can be a good candidate for high-sensitivity and high-precision nondestructive testing of SPMs.