The mechanism of free radical chain reaction in lipid oxidation has been summarized. In addition, the role of endogenous trace constituents, such as oxygen, water, free fatty acids, monoacylglycerol and diacylglycerol, etc, on the oil oxidation has been highlighted. The existence of association colloids self-assembled by the surface active minor constituents in vegetable oil and the corresponding action on oil oxidation has all been discussed. The limiting the presence of pro-oxidants and the degrading of antioxidants should be limited strictly during oil refining, for the critical control point to enhance vegetable oil quality.