The invention relates to a preparation method of calcium phosphate-coated magnesium powder. According to the method, a deposition solution prepared from calcium nitrate, monopotassium phosphate and disodium ethylene diamine tetraacetic acid in a certain ratio is used, and gas-atomized pure magnesium powder is used for a deposition reaction under the deposition conditions that the pH value ranges from 3.6 to 4.8, the deposition temperature ranges from 10 DEG C to 20 DEG C and the stirring speed ranges from 200 rpm to 400 rpm. With the preparation method, a complete and uniform coating layer is prepared on the surface of the pure magnesium powder, the main phase of the coating layer is dicalcium phosphate dihydrate and a small amount of magnesium hydrogen phosphate, and the corrosion resistance of the magnesium powder in a chlorine-containing environment can be improved.