Abstract: Magnesium-ion batteries emerge as a promising candidate in the energy storage field because of its high specific capacity, rich resources, environmental friendliness and excellent safety (dendrite-free). However, the magnesium metal anode is easily passivated in the liquid electrolyte, resulting in the poor electrochemical performance. Therefore, developing highly efficient and applicable solid electrolytes is essential for the realization of high-performance and practical magnesium ion batteries. In recent years, polymer based solid electrolytes have been rapidly developed. This article reviews the ionic conductivity of polymer-based magnesium ion solid electrolytes at home and abroad, the contribution to solving the passivation effect of magnesium metal anodes, and the research progress of its application in magnesium ion batteries. This article summarizes recent advance in polymer-based magnesium ion solid electrolyte, in terms of ionic conductivity, contribution to solving the magnesium anode passivation and application in Mg-ion batteries. Polymer electrolyte has excellent mechanical/electrochemical/thermal stability, high ionic conductivity, and low cost. However, the high charge density and strong solvation of magnesium ions limit its dissociation and diffusion in solid electrolytes. Also, the surface passivation issue of Mg metal anode has not been fully addressed in polymer-based solid electrolyte. This review will enable researchers to quickly grasp the current challenges and feasible solutions in the research of solid magnesium ion electrolytes, and provide guidance for the development of electrolytes in the future.