Abstract: Photoacoustic tomography (PAT) combines the advantages of pure optic imaging and pure ultrasound imaging. It has a potential to become a novel noninvasive medical imaging technology. We have explored filters of RL, SL, Modi-SL and Kwoh-Reed, which influences on photoacoustic imaging. The result of simulations and experiments show that Kwoh-Reed can restrain noise effectively and improve the contrast of images. A Q-switched Nd:YAG laser operating at 532 nm was used as light source. The laser had a pulse width of 7 ns and a repetition frequency of 30 Hz. A needle PVDF hydrophone with diameter of 1 mm was used to detect photoacoustic signals.