The common organic acids on the market are selected, including monoisocaprylic acid, n-caprylic acid, isononanoic acid, neocapric acid, lauric acid and myristic acid, dibasic sebacic acid and undecanedioic acid, and tribasic acid TC65. The lubrication properties of organic acids commonly used in the fully synthetic system of metalworking fluid were evaluated by a four-ball friction testing machine and a tapping torque meter. The results showed that dibasic acids had the strongest ability to lower pH in the fully synthetic formulation at the same concentration. Among the monobasic acids, the commonly used lauric acid has the best lubrication performance in steel processing, and myristic acid has the best lubrication performance in aluminum processing, but the defoaming performance of both is poor. At the same time, for steel machining, with the increase of carbon chain length, the lubrication performance increases, but the branch chain will affect the lubrication of steel workpieces. When the number of carbon chains is greater than 10, regardless of the branched chain and straight chain structure, it has a significant effect on the lubrication of aluminum processing.