A method for improving the carnosic acid content in a rosemary fat-soluble antioxidant belongs to the technical field of plant extraction. The method uses rosemary leaves as a raw material, and comprises the following steps of: preparing a rosemary extract, preparing a carnosic acid crude extract, preparing a carnosic acid refined solution, preparing a carnosic acid eluent, preparing a rosemary extract refined product and preparing a regenerated D370R or D315 anion exchange resin column, thereby preparing a rosemary extract refined product with the carnosic acid content exceeding 90%. In the method provided by the invention, a ceramic membrane is used for separating macromolecular impurities in the rosemary extract, and D370R or D315 weakly basic anion exchange resin is used for separatingand purifying carnosic acid in the rosemary extract, so that the separation specificity is strong, the separation efficiency is high, and the yield is high; the rosemary waste leaves and other byproducts generated in an implementation process are subjected to deep processing treatment, thus realizing comprehensive utilization and environmental protection; and the operation condition is mild, theproduction cost is low, and the prepared product can be widely applied to the fields of food, health products, medicines and the like.