The invention discloses a method for preparing zinc electrodeposit under an ammoniac system. The method comprises steps as follows: ground zinc oxide ore powder is added to pure ammonia water, the mixture is contained in a closed container at the normal temperature and under the normal pressure for leaching of zinc, a leached zinc ammonia complex aqueous solution is reduced with zinc powder, impurities in the leached solution are removed, and a purified zinc ammonia complex solution is obtained; the zinc ammonia complex solution is heated and then subjected to flashing for ammonia removal, zinc-containing slurry is obtained, flashing gas is recovered, and ammonia water is obtained; concentrated sulfuric acid is added to the zinc-containing slurry, and the zinc-containing slurry is changed into a zinc sulfate solution; the zinc sulfate solution is added to an electrolytic bath, a mixture of gelatin, tetramethyl ammonium chloride, benzyl trimethyl ammonium chloride and benzyl triethyl ammonium chloride is added as an additive, an aluminium alloy plate is used as a cathode, a lead alloy plate is used as an anode, electrodeposition is performed, and zinc electrodeposit is obtained. The zinc electrodeposit obtained with the method is high in quality, the efficiency is good, and the energy consumption is low.