TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The method for pre-processing the swill oil comprises: (a) heating the swill oil to 100-110 degrees C, centrifuging for 10 minutes at 4000 rotations per minute, or allowing to stand for 1-3 hours for layering, removing the water and residue at the lower layer to obtain an impurity-removed swill oil at the upper layer; (b) heating the impurity-removed swill oil to 80-90 degrees C, adding soft water (30 wt.%), stirring uniformly and mixing, layering by centrifuging for 20 minutes at 4000 rotations per minute, or allowing to stand for 1-3 hours to remove the water and pectin at the lower layer to obtain a pectin-removed swill oil; (c) performing dewatering treatment to the pectin-removed swill oil to obtain a dried swill oil, where dewatering is carried out by heating to 105 degrees C to evaporate or dewatering using a drying agent by adding drying agent A in swill oil and filtering to obtain a filtrate, where the drying agent A is anhydrous magnesium sulfate or 4A molecular sieve; (d) heating the dried swill oil to 55-65 degrees C, adding hydrogen peroxide (35 wt.%) to the swill oil (2-3 wt.%), mixing and oscillating for 10-30 minutes, and standing 1-5 hours for layering to obtain the supernatant, which is the preprocessed swill oil. The centrifuging time is for 10-20 minutes at 4000 rotations per minute. The amount of sodium hydroxide used is 0.8-1.0 wt.% and potassium hydroxide is 1.3-1.8 wt.% of that of the preprocessed swill oil. The acid-base neutralization method comprises: adding hydrochloric acid with the amount being 4 divide by 5-9 divide by 10 of that of the matter added into the catalyst into the reaction liquid, stirring for acid-base neutralization; and adding hydrochloric acid until the pH is 6.8-7.2, where the mass concentration of the hydrochloric acid is 25-38%. The water washing method in step (iii) comprises: adding supernatant, adding 1 divide by 3 volume units of pure water to wash for 3-5 times, separating foam and water by a separating funnel, and drying the water washed liquid with a drying agent B. The drying in step (iii) comprises: pouring the water washed liquid into a container containing A4 molecular sieve, oscillating or stirring for 10-15 minutes, sealing to stand and drying for 3-5 hours and filtering the dried liquid by filter paper to obtain the filtrate. The distillation in step (iii) comprises: heating the filtrate to 80 degrees C, evaporating for 30 minutes, and removing remaining methyl alcohol to obtain the marine bio-diesel product.