Magnesium alloy is the lightest structural metal material. As its ductility is usually limited because of its hexagonal closest packing (hcp) structure, it is significant to improve its forming performance. The primary way to achieve this goal is by grain refinement. This study explores new ways of grain refinement for cold-rolled sheet of magnesium alloy AZ31B by probing into its structural evolvement in heat treatment. It is found that recrystallization mostly takes place in the cold-rolled sheet in heat-treatment, and refined and equiaxial recrystallization grains with an average diameter of (14 to 15) mm can be obtained by heat-treatment at 260 C for (60 to 90) min, which is an effective method to obtain refined symmetrical grains of magnesium alloy by heat treatment at a lower recrystallization temperature after cold-rolling. Magnesium alloy is the lightest structural metal material. As its ductility is usually limited because of its hexagonal closest packing (hcp) structure, it is significant to improve its forming performance. The primary way to achieve this goal is by grain refinement. This study explores new ways of grain refinement for cold-rolled sheet of magnesium alloy AZ31B by probing into its structural evolvement in heat treatment. It is found that recrystallization mostly takes place in the cold-rolled sheet in heat-treatment, and refined and equiaxial recrystallization grains with an average diameter of (14 to 15) mm can be obtained by heat-treatment at 260 C for (60 to 90) min, which is an effective method to obtain refined symmetrical grains of magnesium alloy by heat treatment at a lower recrystallization temperature cold-rolling.