The grain refinement mechanisms of Sr in the AZ31 magnesium alloys were studied by both phase diagram calculation and experimental analysis.The influence of Sr content on the solute distribution coefficients of Al and Zn during solidification was investigated in order to find out whether Sr addition can enhance the grain refinement efficiency brought by Al and Zn.The results showed that Sr addition can promote the segregation in liquid phases for both Al and Zn during solidification,therefore enhance the grain refinement effects by Al and Zn in AZ31 magnesium alloys.And the effect of Sr addition on the solute distribution coefficients for Al is larger than that of Zn.Sr addition can improve the GRF values by itself and also improve the GRF values of Al and Zn to the AZ31 magnesium alloys,and the grains are refined consequently. The grain refinement mechanisms of Sr in the AZ31 magnesium alloys were studied by both phase diagram calculation and experimental analysis. The influence of Sr content on the solute distribution coefficients of Al and Zn during solidification was investigated in order to find out whether Sr addition can enhance the grain refinement efficiency brought by Al and Zn.The results showed that Sr addition can promote the segregation in liquid phases for both Al and Zn during solidification, therefore enhance the grain refinement effects by Al and Zn in AZ31 magnesium alloys. And the effect of of Sr addition on the solute distribution coefficients for Al is larger than that of Zn. Sr addition can improve the GRF values ​​by itself and also improve the GRF values ​​of Al and Zn to the AZ31 magnesium alloys, and the grains are refined than.