The invention relates to a covering agent used for vertical semi-continuous casting of aluminum bronze and application thereof. The covering agent consists of the following components in percentage by weight: 40 to 70 percent of cryolite, 2 to 10 percent of phosphor copper master alloy and the balance of charcoal ash, wherein the summation of the percentage by weight of each component is 100 percent. When the covering agent is applied to the vertical semi-continuous casting of the aluminum bronze, a 'thin covering' technique is adopted, namely a round porous mesh screen is fixed on a crystallizer, the cover agent is placed in the mesh screen, and during casting, along with the vibration of the crystallizer, the powdered covering agent in the mesh screen is uniformly scattered on the surface of a fused mass, and the covering thickness is only 0.5 to 2 mm. The covering agent not only can reduce the defects of slug inclusion on an ingot casting surface layer, gas holes, cold shut and thelike, but also can reduce the depth of the slug inclusion in an ingot, so the ingot surface quality is high, the finished product rate is improved by 10 to 40 percent, and the ingot has high mechanical properties. When applied to the casting of the aluminum bronze, the covering agent can also improve the production efficiency of casting of the aluminum bronze by 15 to 35 percent, and prolong the service life of the crystallizer by 50 to 80 percent. The covering agent is simple and convenient to prepare, has a low use cost, and is simple for production operation.