TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Device: The device for washing comprises a plate-type centrifugal machine, a homogeniser, a blending tank of semi-finished product of biodiesel, a washing water storing tank, a circulation pump, and other pipe parts, and control valves. The device for drying the biodiesel comprises a blending tank of semi-finished product of biodiesel, a pre-heater, a membrane evaporator, a plate heat exchanger, a temporary storing tank of finished product of biodiesel, a finished product transferring pump, a temporary storing tank of waste water, a waste water pump, a vacuum pump, a gas-liquid separator, a heat-conducting oil heating furnace, a heat-conducting oil circulation pump, a transmission pump, a heat-conducting oil expansion slot, a cooling water tower, a cooling water circulation pimp, a pipeline, and a control valve.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Composition: The dosage of potassium hydroxide is 0.5-0.6% of total quantity of the animal and plant greases; and the dosage of the methanol is 18-20% of total quantity of the animal and plant greases. Preferred Conditions: Transesterification is carried out for 6-12 hours. Preferred Process: In (b), the reaction product after transesterification is persistently transmitted to a plate-type centrifugal machine to centrifuge and separate; where the light biodiesel is held in central part of plate body of the centrifugal machine and it is pushed and entered into a pipeline and entered into a homogenizer through a control valve to contact with washing water; and the washing water is transmitted to the homogenizer from a washing water storing tank through a transmitting pump and a control valve, and heavy saponification glycerin mixture is discharged from the centrifugal machine. In (c), the washed biodiesel is transmitted to the blending tank of semi-finished product of biodiesel; where the materials are transmitted to the plate-type centrifugal machine to separate through a control valve; the said biodiesel is held in central position of the centrifugal machine during the process for centrifuging at a high speed under such a condition that proportion of the biodiesel is small; the biodiesel is discharged from the centrifugal machine and entered into the homogenizer; the washing water comprising biogel is simultaneously pushed outside the plate-type centrifugal machine according to large proportion; and the washing water is discharged from the centrifugal machine and persistently pushed outside the centrifugal machine through a control valve. Vacuum drying with membrane comprises transmitting semi-finished product of biodiesel to the pre-heater to exchange heat with heat-conducting oil; where the semi-finished product of biodiesel separated from the pre-heater is controlled at 95 degrees C; and entering into the membrane evaporator; where the biodiesel entered into cylinder of the biodiesel is symmetrically coated in the cylinder of the biodiesel in the form of thin film; the moisture within the biodiesel is vaporized at 95 degrees C to enter to the heat exchanger outside the same and to condense; and the biodiesel film that cannot be vaporized is slid down and fallen into the temporary storing tank of finished product of biodiesel along inner wall of the cylinder of biodiesel.