The influences of the acoustic refraction cause by the mismatch of ultrasonic velocities on photoacoustic image were studied. We have explored the acoustic velocity matching in image reconstruction. The experiments demostrated that the matching acoustic velocity greatly improved the contrast of the reconstructed image and obviously reduced the background artifacts;the spatial resolution of the reconstructed image was improved from 0. 50 mm to 0. 15 turn. Our study has great practical significance for applying photoacoustic tomography to norvinvasive clinic diagnosis of cancer.