Disclosed are auxiliary for increasing yield of light oil in oil catalytic cracking device, and a preparation method of the auxiliary. The auxiliary is made of agent A, agent B, C24H44N4 and solvent oil, wherein the agent A is made by reacting of rare earth and glacial acetic acid, and the agent B is made by reacting of fatty acid, hydrogen peroxide and antimony compound. By the aid of the auxiliary, the yield of light oil can be increased by 3.06%, the yield of coke is reduced by 0.4%, and the yield of heavy oil is reduced by 1.95%. By the aid of the auxiliary capable of replacing metal deactivator, economic benefit increase, energy conservation and carbon dioxide emission reduction can be achieved without changing existing operation conditions of the catalytic cracking device.