The work aims to study the microstructure of the hot dip Al-Zn plated coating. Scanning electron microscope, energy spectrum and electron probe are used to analyze the structure and composition of the surface of the aluminum zinc plate and the coating. X-ray diffraction and electron backscatter diffraction are used to analyze the phase composition and phase structure of the Al-Zn plate coating. The surface of the Al-Zn plate is a typical spangle morphology, and the interior of the zinc flower shows a structured dendrite structure. The Al-Zn plate coating is divided into an inner layer and an outer layer along the thickness direction, the outer layer is an alloy layer which is mainly composed of Al, Zn and Si. The layer is mainly composed of Al-rich phase, Zn-rich phase, and a small number of strip-shaped high Si phase. The inner layer in contact with the steel substrate is a intermetallic compound layer. The thickness of this layer is only about 1 μm and its composition is Fe, Al and Si which is composed of densely dispersed fine particles and a small amount of dispersed coarse particles. In addition, a small amount of high Si phase in the form of strips or particles was found between the transition layer and the alloy layer. The phase structures of the Al-rich phase, Zn-rich phase, and strip high Si phase of the alloy layer in the Al-Zn plate coating are Al face-centered cubic structure, Zn close-packed hexagonal structure and Si face-centered cubic structure respectively. The distribution characteristics of the high Si phase can effectively control the thickness of coating. The phase structure of the transition layer is more inclined to the monoclinic Al13Fe4. During the formation of this layer, part of the fine particle phase grows and coarsens, thereby forming a coarse particle phase, interposed between the transition layer and the alloy layer, which further strengthens the transition layer and the alloy layer. The connection indirectly plays a key role in improving the adhesion and elongation of the coating.