Abstract: Photoacoustic imaging(PAI) is a state of the art biomedical imaging technique with the potential of wide application. Based on the photoacoustic effect, PAI combines the advantage of optical imaging as high contrast and spectroscopic specificity with the advantage of ultrasonography as high spatial resolution and deep penetration. This paper introduced the latest progress in PAI, which contains the fundamentals of photoacoustic imaging, the improvement in detecting modes of images, and the most promising clinical applications. The limitation of PAI has also been discussed.