Twelve acid diethanolamide boric acid ester was prepared by using twelve acid and diethanolamine and boric acid as raw materials,and its structure was analyzed by using Fourier Transform Infrared Spectrometer.A semisynthetic cutting fluid was prepared by adding a certain amount of boric acid ester into the base oil,the corrosion performance and antirust property were analyzed,and the extreme pressure and antiwear properties were tested by four ball friction testing machine.The results show that the prepared borate ester has good extreme pressure and antiwear properties in semisynthetic cutting fluid,when the mass fraction of boric acid ester is 11.3%,the friction coefficient of 5% diluent of the cutting fluid reaches 0.056 and maximum nonseizure load reaches 392 N.The performance indicators of the semi synthetic cutting fluid with the borate ester as additive meet the national standard of GB/T 6144-2010.