The invention belongs to the technical field of biodiesel, and particularly relates to a device and method for preparing biodiesel through superheated ethanol vapor without a catalyst. The device comprises a reactor, and the top of the reactor is provided with a feed port and a discharge port; the discharge port is sequentially communicated with a condenser, a dryer, an ethanol recycling tank, a heater and a superheater through pipelines, the superheater is communicated with the reactor through a feed pipe which penetrates through the feed port to extend to the bottom of the reactor, the end, stretching into the reactor, of the feed pipe is connected with an annular pipe, and the annular pipe is provided with an air hole. The method comprises the steps that grease is added into the reactor, the temperature is increased, the superheated ethanol vapor prepared through the heater and the superheater is introduced into the reactor, a micro-positive pressure reaction is kept, the superheated ethanol vapor which does not take part in the reaction and water vapor generated in the reaction enter the condenser to be condensed and then enter the dryer to remove moisture, and ethanol enters the ethanol recycling tank. The device has the advantages that the structure is simple, the design is reasonable, no catalyst is used, no tedious pretreatment stage is needed, and the conversion rate is high.