Abstract: In this paper, the basic imaging principles of optical microscope, scanning electron microscope and atomic force microscope are analyzed.The fresh section and polished surface morphology with different scales of coal samples are characterized by three kinds of microscopes.The results show that under the optical microscope, blurred areas often appear in the observed images due to the different distances from the focal points to the fresh sections.The surface of polished coal sample is flat, its imaging effect is relatively good, and the different components of coal can be qualitatively analyzed.The images obtained by scanning electron microscope can be continuously amplified and 3D structure can be displayed by 2D image, then more detailed microsurface information can be observed.The observation of microsurface morphology of polished sample can be used to qualitatively analyze different components of coal.Compared with 2D images, the 3D images obtained by atomic force microscope can display the microsurface morphology more intuitively, and the microsurface roughness, height difference and its statistical distribution can be accurately obtained.Atomic force microscope can characterize the nano crack and its width in detail, and the widths in the three sections of the crack are 21.63 nm, 17.31 nm and 8.66 nm, respectively.In the study on surface morphology of coal samples, if the microscopic characterization of optical microscope, micronscale scanning of scanning electron microscope and nanoscale detection of atomic force microscope are combined, the characteristics of samples from whole to local and from millimeter to nanometer can be accurately expressed, and relatively comprehensive and continuous information can be obtained.