NOVELTY - Preparation of biological diesel oil involves mixing oil feedstock, alcohol and catalyst, and performing ester exchange reaction; separating crude solution of biodiesel and crude glycerin solution in separation column; entering biodiesel crude solution and crude glycerin solution in electrodialysis apparatus, separately; entering crude biodiesel and crude glycerin in distiller, recovering alcohol, and entering remaining solution in refined biodiesel filter stage and glycerin distillation stage; filtering both solutions, and entering into bio-diesel collection tank and glycerin collection tank.    USE - Method for preparing biological diesel oil (claimed).    ADVANTAGE - The method ensures catalyst recovery rate of more than 97%, ensures purity of biological diesel oil at 98.4% and purity of glycerol at 98%. It has simple technique, easy operation, high efficiency, no pollution, low energy consumption, and clean and semi continuous process.    DETAILED DESCRIPTION - Preparation of biological diesel oil comprises taking oil feedstock from feed tank (1), alcohol from alcohol tank (2) and catalyst from catalyst tank (3), mixing in main reaction tank (4), and performing ester exchange reaction at 140-200 degrees Cfor 2-3 hours; entering into main product tank (5), and separating crude solution of biodiesel and crude glycerin solution in separation column; separating biodiesel crude solution in electrodialysis apparatus, and recovering alcohol and catalyst; entering crude glycerin solution in electrodialysis apparatus, and recovering alcohol and catalyst; entering crud biodiesel in distiller, recovering alcohol, and entering remaining solution in refined biodiesel filter stage; entering crude glycerin in distiller, recovering alcohol, and entering remaining solution into glycerin distillation stage; filtering obtained solutions to remove impurities, and entering into bio-diesel collection tank and glycerin collection tank. An INDEPENDENT CLAIM is included for biological diesel oil processing device comprising electrodialysis apparatus, direct power supply, catalyst reaction product outlet pipe, alcohol outlet tube, reaction product inlet tube, alcohol inlet, positive electrode, negative electrode, cation exchange membrane, anion exchange membrane, alcohol flow channel, reaction product channel, cation exchange membrane, and anion exchange membrane.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of biological diesel oil preparation device.    Feed tank (1)    Alcohol tank (2)    Catalyst tank (3)    Main reaction tank (4)    Main product tank (5)