Abstract: Provided in the present invention is a method for improving the yield of enzymatic preparation of biodiesel from greases, comprising: during enzymatic reaction of short-chain alcohols with greases to prepare biodiesel, introducing online dehydration steps, which lead the volatile gases in the enzyme reactor to enter into the low-temperature absorption tank, and the dehydrated gases flow back into the enzyme reactor. The formation of gas-circulation can constantly bring the moisture inside the enzyme reactor out.