Photoacoustic imaging (PAI) is a new non-invasive and non ionizing biomedical imaging method developed in recent years. When the pulse laser irradiates the biological tissue, the light absorption domain of the tissue will produce the ultrasonic signal. The light acoustic signal generated by the biological tissue carries the light absorption characteristic information of the tissue. By detecting the light acoustic signal, the light absorption distribution image in the tissue can be reconstructed. It can break through the “soft limit” (~ 1 mm) of high-resolution optical imaging depth and realize the imaging of 50 mm deep tissue in vivo.