TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The raw oil comprises acid oil, drainage oil, fried oil and microbial oil. Preferred Method: The esterification reaction step comprises primary esterification step and secondary esterification step. The primary dehydration step comprises adding the raw oil into a first kettle and starting stirring, turning on a vacuum system, heating the dehydrated oil, measuring the acid value when the moisture content is lower than 0.1% and compounding acid-methanol mixture to the acid value. The primary esterification step comprises adding the well measured acid-methanol mixture into the first kettle, starting stirring and heating up to 100-110 degrees C, turning on the valve A of a second kettle to a gasification methanol tower, turning on the valve of B from first kettle to second kettle, pressing methanol material into the second kettle by an internal pressure of first kettle slowly, closing valve B, starting stirring of second kettle, heating and methanol removing, stop stirring after the whole methanol is removed and standing for 30 minutes, draining the acidic water, measuring the acid value, where the acid value is required to be less than 10 mg potassium hydroxide (KOH)/g. The secondary esterification step comprises heating the material in the second kettle to 100 degrees C, adding a little more acid (0.1-0.2%), regulating the flow of methanol well and spraying in methanol slowly for 10-30 minutes, sampling and measuring the acid value, stopping spraying, when the acid value is less than 2 mg KOH/g, removing the excessive methanol, stopping stirring, standing for 15 minutes and draining the acidic water. The secondary dehydration step comprises driving the material in first kettle to third kettle and performing vacuum dehydration. The alkali collocation step is carried out at a moisture content of less than 0.1% and acid value of less than 2 mg KOH/g. The transesterification reaction step comprises driving the alkali-methanol mixture to third kettle and performing transesterification reaction after stirring for 30 minutes, sampling and detecting the production of glycerol, removing the excessive methanol after the production of glycerol in normal condition, removing methanol at a temperature of lower than at 90 degrees C, stopping stirring, standing for 30 minutes, and separating glycerol. The purifying step comprises driving the crude fat acid methyl ester separated from glycerol to biodiesel distilling tower for refining to obtain biodiesel products.