The present disclosure provides a magnesium alloy and a preparation method and an application thereof. Based on the total weight of the magnesium alloy, the magnesium alloy includes 2-3.5 wt % of Ce, 0.01-0.2 wt % of R, 0.8-1.5 wt % of Mn, 0-0.01 wt % of Fe, 0-0.01 wt % of Cu, 0-0.01 wt % of Ni, 0-0.01 wt % of Co, 0-0.01 wt % of Sn, 0-0.01 wt % of Ca, and 94.74-97.19 wt % of Mg, wherein R is at least one selected from Al and Zn.