NOVELTY - Preparation of biodiesel involves preparing carbon-based sulfonic acid-functionalized solid acid catalyst, adding peanut oil, soybean oil, sesame oil, rape seed oil or cotton seed oil in a reactor, then adding methanol, ethanol or propanol, and carbon-based sulfonic acid-functionalized solid acid catalyst, carrying out transesterification reaction at 90-160 degrees C for 1-8 hours, separating the catalyst, subjecting the filtrate to liquid separation, washing, separating the organic phase, drying the organic phase, filtering, and distilling under reduced pressure.    USE - Preparation of biodiesel (claimed).    ADVANTAGE - The biodiesel is prepared with high yield under mild conditions, without side reaction such as saponification reaction by simple and environmentally-friendly process.    DETAILED DESCRIPTION - Preparation of biodiesel involves adding 5-20 ml solvent, 5 g glucose, and glucose dissolved in 30-60 ml sulfuric acid into 250 ml three-necked flask provided with electric mixer and reflux condenser, heating the mixture at 120-170 degrees C for 3-15 hours under protection of nitrogen, cooling the reaction mixture to room temperature, washing the cooled product using 1000 ml deionized water, filtering, washing the filtrate using deionized water at 80-90 degrees C, further washing using ethanol until the wash liquid does not detect sulfate, drying the resultant black solid in an electric-heated blast oven at 90-120 degrees C for 10-20 hours, cooling the resultant product and grinding into powder to obtain carbon-based sulfonic acid-functionalized solid acid catalyst, adding peanut oil, soybean oil, sesame oil, rape seed oil or cotton seed oil in a reactor, then adding methanol, ethanol or propanol, and carbon-based sulfonic acid-functionalized solid acid catalyst, carrying out transesterification reaction at 90-160 degrees C for 1-8 hours, separating the catalyst by filtering the reaction mixture, subjecting the filtrate to liquid separation such that lower glycerol, and upper layer product containing 5-10% sodium bicarbonate are separated, washing, separating the organic phase, drying the organic phase using anhydrous magnesium sulfate, filtering, and distilling under reduced pressure. The content of catalyst is 1-15% with respect to the peanut oil, soybean oil, sesame oil, rape seed oil or cotton seed oil. The molar ratio of methanol, ethanol or propanol, and peanut oil, soybean oil, sesame oil, rape seed oil or cotton seed oil is 6:1-40:1.