Disclosed herein relates to biopharmaceuticals, and more particularly to a continuous flow method for preparing (R)-3-hydroxy-5-hexenoate. Carbonyl reductase and isopropanol dehydrogenase are co-immobilized onto an inert solid medium simultaneously to prepare a carbonyl reductase/isopropanol dehydrogenase co-immobilized catalyst, which is then filled into a microchannel reactor of the micro reaction system. A solution containing substrate 3-carbonyl-5-hexenoate is subsequently pumped into the microchannel reactor to perform an asymmetric carbonyl reduction reaction to obtain (R)-3-hydroxy-5-hexenoate.