TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The short chain alkanol is ethanol, propanol, butanol, pentanol or branch-chain alkanol. The branch-chain alkanol is isopropanol (preferably) or isobutanol. The oil is plant oil, animal oil, microorganism grease, microalgae grease, restaurant recycled oil, plant oil refined oil foot, acidized oil and other common greases and grease by-products. The reaction catalyst of the fraction rich in saturated fatty acid and short chain alkanol or branch-chain alkanol is 98% concentrated sulfuric acid; and the reaction condition comprises 98% concentrated sulfuric acid, at ratio of fatty acid to short-chain alkanol (mol/mol) of 1:3-5, ratio of fatty acid to concentrated sulfuric acid at 47-50:1, at 60-65 degrees C for 5-6 hours. Preferred Processes: The raw material oil is hydrolyzed and separated by urea adduction fractionation to obtain a fraction rich in saturated fatty acid and fraction rich in unsaturated fatty acid. The urea adduction fractionation comprises measuring amount of free fatty acid, urea and methanol at ratio of free fatty acid to urea (W/W) at 1:0.5-3 and ratio of the free fatty acid to methanol (W/V) at 1:4-6; and adding urea to methanol, agitating until urea fully dissolved, controlling temperature at 50-60 degrees C, adding free fatty acid, agitating for 40-50 minutes, boiling for 1-5 hours at 0-20 degrees C, separating crystals, filtering and leaching by methanol; washing by hot saturated sodium chloride solution for 2-3 times until oil phase is clear and transparent, drying by anhydrous sodium sulfate, and obtaining the fraction rich in saturated fatty acid; and decompressing and distilling filtrate at 50 degrees C to recycle solvent, washing by hot saturated sodium chloride solution for 2-3 times until oil phase is clear and transparent, drying by anhydrous sodium sulfate, and obtaining fraction rich in unsaturated fatty acid. The reaction of the fraction rich in saturated fatty acid and the short-chain alkanol further comprises enzymatic reaction or chemical reaction.