The invention belongs to the technical field of alloy sacrificial anode preparation, and relates to a preparation method for delaying the corrosion rate of a magnesium alloy sacrificial anode. The method comprises the following steps of heating the magnesium ingot by an electric furnace until the magnesium ingot is melted, and continuously heating to melt the aluminum ingot and the zinc ingot; heating and adding anhydrous manganese chloride, stirring, adding a refining agent, refining and removing impurities; standing and cooling, and settling part of impurities, heating, adding the magnesium-mixed rare-earth alloy, continuously refining after melting, and then introducing protective gas; cooling, and casting with a water-cooled mould, and a magnesium alloy sacrificial anode is obtained; and the magnesium alloy sacrificial anode is preheated and then is subjected to an integral impregnation process, then the magnesium alloy sacrificial anode is dried and cooled, the local position glueis removed, and the position of the removal glue is exposed. After the magnesium alloy is cast and formed, all the whole magnesium alloy is impregnated with the impregnation equipment, and then the part needing to be exposed is cut, so that the contact surface of the magnesium alloy corroded by corrosion is small, through practice, the corrosion rate of the magnesium alloy anode can be delayed, and the protection time can be prolonged to be 2 times to 3 times that of the original magnesium alloy anode.