Photoacoustic microscopy is a fast-developing imaging technology, which depends on the optical absorption differences and inherits high contrast of optical imaging and deeper depth of ultrasound imaging. Thus, photoacoustic microscopy presents more merit than optical microscopy. Photoacoustic microscopy realizes multiscale imaging from acoustical resolution to the optical resolution, which provides multi-parameters imaging from simple absorption structure to its function, multi-contrast imaging from endogenous contrast agents to exogenous contrast agent, and imaging from ultrasound-transducer-based to all-optical excitation and detection, and multimodality imaging combined with optical coherence tomography, fluorescence imaging, two-photon imaging, second harmonic imaging, etc. Photoacoustic microscopy is widely applied in the field of biomedicine, such as vascular biology, oncology, neurology, ophthalmology, dermatology, and so on.