NOVELTY - Preparing negative 10 NO. biodiesel from waste oil based on rectification technique comprises taking waste oil as main material and adding in catalyst like methanol and sulfuric acid and reacting to get the product.    USE - The method is useful for preparing negative 10 NO. biodiesel from waste oil based on rectification technique (claimed).    DETAILED DESCRIPTION - Preparing negative 10 NO. biodiesel from waste oil based on rectification technique comprises taking waste oil as main material and adding in catalyst like methanol and sulfuric acid and reacting to get the product, specifically, the method comprises: (a) technique flow: choosing material, hydrolyzing, fractionating, esterifying, neutralizing, dealcoholizing and rectifying and finally obtaining finished product; (b) choosing waste animal and plant oil as materials and clean water to throw into the oil counter current hydrolyzing tower to hydrolyze; (c) reacting for 4-8 hours with the hydrolyzing reaction temperature of 200-250 degrees C, pressure of 2.5-3.0 MPa and ratio of oil and water of 1:0.4-0.5, and then separating to obtain coarse fatty acid and glycerol aqueous solution; (d) taking the coarse fatty acid to throw in the fractionating tower to fractionate with the reaction conditions that vacuum residual voltage inside the tower is smaller than 2 mm mercury and distilling temperature is 200-250 degrees C, fractionating the fatty acid to obtain mixture of oleic acid, linoleic acid and linolenic acid and by-products palmitic acid and stearic acid; (e) taking the mixture of oleic acid, linoleic acid and linolenic acid to mix with methanol, adding with sulfuric acid to react for 4-8 hours with the esterification reaction temperature of 70-85 degrees C to obtain carboxylate and water; (f) adding sodium carbonate to the carboxylate to remove dissociative acid and then remove methanol and recycle it; and (g) pumping the dealcoholized carboxylate into the fractionating tower to fractionate with the reaction conditions that vacuum residual voltage inside the tower is smaller than 5 mm mercury and reacting temperature is 200-250 degrees C, and removing residues to obtain finished product of biodiesel.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the method for preparing negative 10 NO. biodiesel from waste oil based on rectification technique. Drawing includes non-English language text.