Mg alloys are the lightest metal structure material for large-scale applications. Elucidating the evolution mechanisms of Mg alloy‘s microstructures during preparation and service condition is critical to obtain high performance magnesium alloy products. Synchrotron radiation imaging technique with high temporal and spatial resolution can realize in-situ dynamic observation of microstructure evolution of alloys during preparation and in simulated service environment. This article reports the recent research progress in the microstructure evolution mechanisms of Mg alloy with the application of synchrotron radiation imaging technique. The crystal evolution behavior of Mg alloys during solidification, the formation and propagation of cracks under complex loading condition and microstructure evolution in biocorrosive environment are discussed. The magnesium alloy dendrite morphology is influenced by alloying elements and solidification conditions. Microcracks are inclined to initiate on the second phase surface and extend along the particles aggregation area. Mg alloys show good biocompatibility under biological corrosion environment, and the degradation rate can be controlled by surface modification. In addition, the advantage and limitation of synchrotron radiation imaging technique in these research are analyzed briefly, providing a new promising way for the investigation of microstructure in Mg alloy and other alloys. In the end, the research trends of synchrotron radiation imaging technique in the study of Mg alloys are prospected.