NOVELTY - Preparation of biodiesel oil comprises taking lipid, fatty alcohol and solid alkali into reaction kettle, heating in water bath, performing transesterification reaction at 50-80 degrees C and 2-6 MPa at reaction liquid volume space velocity of 0.3-4/hour, adding into distillation tank, distilling fatty alcohol, separating glycerol, adding 0.1-10% non-ionic surfactants as filter aid, and separating fatty acid glyceride by ceramic film at 10-120 degrees C and cross film pressure difference of 0.08-0.5 MPa to obtain high-purity biodiesel oil.    USE - Method for preparing biodiesel oil (claimed).    ADVANTAGE - The method has simple technique, good raw material adaptability, high yield and no matter accumulation problem. The transesterification reaction is done at low temperature and pressure, thus reducing cost.    DETAILED DESCRIPTION - Preparation of biodiesel oil comprises taking lipid, fatty alcohol and solid alkali into reaction kettle, heating in water bath, performing transesterification reaction at 50-80 degrees C and 2-6 MPa at reaction liquid volume space velocity of 0.3-4/hour, adding into distillation tank, distilling fatty alcohol, separating glycerol, adding 0.1-10% non-ionic surfactants as filter aid, and separating fatty acid glyceride by ceramic film at 10-120 degrees C and film pressure difference of 0.08-0.5 MPa to obtain high-purity biodiesel oil. The solid alkali is zinc oxide (ZnO)/calcium hydroxide Ca(OH)2/potassium fluoride (KF), KF/montmorillonite (MMT) and sodium silicate. The non-ionic surfactant has hydrophilic lipophilic balance value of 3-25. The ceramic film having film aperture of 0.02-1.4 mu m is inorganic carbon film comprising aluminum oxide or titanium oxide. An INDEPENDENT CLAIM is included for preparation of ZnO/Ca(OH)2/KF solid alkali comprising mixing ZnO, Ca(OH)2 and KF dihydrate at mol ratio of 2.0:1.0:(0.5-2.0), adding deionized water, drying at 70-90 degrees C for 5-7 hours and baking at 250-500 degrees C for 5-7 hours.