Human milk fat provides 45%-60% of energy for infants. However， due to the difference in fat structure and content， infant formula milk based on cow’s milk and other vegetable oils has a fat digestion and absorption rate that is 20%-25% lower than that of human milk. Thus， the preparation of alternative lipids similar to the structure and composition of breast milk fat is a research hotspot in the field. This article selected Tibet yak ghee with high similarity to human milk fat as the main raw material， fatty acid ethyl ester as the acyl donor， catalyzed by immobilized lipase RM IM， and then other factors of water activity， sunstrates ratio， reaction time and temperature was optimized by response surface methodology. The optimum reaction conditions were obtained： Tibet yak ghee， sunflower oil ethyl ester and oleic ethyl ester which the molar ratio of was 2.13 ∶ 1 ∶ 1 was catalyzed with 10% RMIM （water activity 0.61） at 68 ℃. In the structured lipids， the content of total linoleic acid and palmitic acid sn-2 of final product in model validation actually were 17.59% and 56.40%， which is in consistent with the predicted value and can be used as another source of breast milk fat substitute. Our results provided new possibilities for the synthesis of human milk fat substitute （HMFS）.