The invention discloses a nanometer confinement high-magnesium alloy and a preparation method thereof. The nanometer confinement high-magnesium alloy comprises, by atomicity, 90% of magnesium, 1-9% ofcerium, and the balance nickel powder. The preparation method comprises the following steps that nickel is pre-pressed into sheets by a tablet press; a graphite crucible is preheated to 100-200 DEG C, and components of magnesium ingots are added to the crucible, the temperature is heated to 550-600 DEG C, protection agent coating is smelted by the magnesium alloy, then the temperature is heated to 790-810 DEG C, and cerium ingots are put into magnesium metal solution with temperature being 790-810 DEG C, and alloy melts are obtained; the alloy melts are heated to 820-850 DEG C, and the pressed nickel sheets is put into the alloy melts with temperature being 820-850 DEG C to obtain Mg-Ni-Ce alloy melts; and the alloy melts are heated to 880-900 DEG C to stay warm until the nickel sheets are melted completely, foam titanium is added into the alloy melts, the foam titanium is taken out to cool in indoor temperature to obtain a nanometer confinement high-magnesium alloy. The nanometer confinement high-magnesium alloy and the preparation method thereof can improve the yield of magnesium alloys, and the quality of magnesium alloys is improved.