A compounding agent for preparing engine lubricating oil is disclosed, and is characterized by being composed of base oil, a disperser, a detergent, an antiwear agent, an antioxidant, a viscosity index improver, a pour point depressant, an anti-foaming agent, a demulsifier, a metal magnesium powder and a metal chromium powder. The disperser is polyisobutene succinimide; the detergent is a phosphate; the antiwear agent is alkyl containing phosphatide and salt; the antioxidant is ainc dialkyl dithiocarbamate; the viscosity index improver is an ethylene-propylene polymer; the pour point depressant is a vinyl-ethylene polymer; the anti-foaming agent is an alkyl acrylate copolymer; and the demulsifier is poly-alkoxyl polyol. The compounding agent for preparing engine lubricating oil comprises the following components in percentage by weight: 12-13% of the disperser, 12-13% of the detergent, 4-5% of the antiwear agent, 14-15% of the antioxidant, 4-5% of the viscosity index improver, 7-8% of the pour point depressant, 6-8% of the anti-foaming agent, 9-10% of the demulsifier, 1-2% of the metal magnesium powder, 1-2% of the metal chromium powder, and the balance of base oil. A method for manufacturing the compound additive for engine lubricating oil disclosed by the invention is simple, economic and practical; and the manufactured product is low in price, high in quality, and capable of prolonging the service cycle of the lubricating oil, enhancing the antiwear and extreme-pressure-resisting effects of the lubricating oil, improving the various effects of oxidization resistance, corrosion resistance and forming resistance of the lubricating oil, keeping the clean effect of the lubricating oil for a long time, and comprehensively enhancing the integrated effect of the engine lubricating oil.