Photoacoustic tomography is a developing, promising，non-invasive imaging method in the medical clinic diagnosis. It is an ultrasound-mediated biophotonic imaging method based on the intrinsic optical absorption properties of tissue and ultrasonic detection, and combines the merits of both high contrast advantage of pure optical imaging and high resolution advantage of pure ultrasound imaging. Photoacoustic tomography can be performed by detecting photoacoustic waves instead of detecting photons. In photoacoustic tomography, imaging contrast is based primarily on the optical properties of biological tissues, and imaging resolution is based primarily on the ultrasonic waves. It can avoid the influence of optical scattering on imaging resolution in principle, and can provide tomography of tissues with high contrast and high spatial resolution at medium depths. Photoacoustic tomography can provide an effective approach to studying the structures, physiological properties, metabolisms, pathological properties of biological tissues. It has important potential clinical applications in the early non-invasive detection of cancers, structural and functional in vivo imaging. A brief introduction of photoacoustic imaging mechanisms is gives, and the imaging methods, the image reconstruction algorithm and the potential biomedical applications of photoacoustic tomography are reveiewed.