NOVELTY - Preparation of biodiesel using grass carp visceral fat involves introducing washed grass carp viscera into ceramic pot, adding distilled water, placing the pot in a magnetic stirrer, stirring, adding hydrochloric acid solution to adjust pH to 3-4 to obtain internal organ mixture, adding pepsin to internal organ mixture, placing mixture in constant-temperature oscillator, enzymolyzing under oscillating conditions, transferring enzymolysis liquid into oven, drying, adding petroleum ether to enzymolysis liquid, heating, extracting and separating to obtain supernatant.    USE - The method is useful for preparing biodiesel using grass carp visceral fat, where the biodiesel is useful as power fuel for truck.    ADVANTAGE - The method ensures environmentally-friendly preparation of biodiesel using grass carp visceral fat with improved oxygen content and combustion performance and without three wastes emission.    DETAILED DESCRIPTION - Preparation of biodiesel using grass carp visceral fat involves (a) introducing 50-100 g washed grass carp viscera into a ceramic pot, adding 300-400 ml distilled water, placing the pot in a magnetic stirrer, stirring at 2000-3000 rpm for 10-15 minutes, adding 10% hydrochloric acid solution to adjust pH to 3-4 to obtain internal organ mixture, (b) adding 2.5-5 g pepsin to internal organ mixture, placing mixture in a constant-temperature oscillator, controlling temperature of oscillator at 28-38 degrees C, enzymolyzing under oscillating conditions for 1-2 hours, transferring enzymolysis liquid into oven, drying at 80-90 degrees C for 5-10 minutes, adding 90-100 ml petroleum ether to enzymolysis liquid, heating in a water bath at 32-35 degrees C, extracting for 2-3 hours and separating to obtain supernatant, (c) placing supernatant in a distillation flask, transferring distillation flask into a water bath, maintaining temperature at 60-65 degrees C, distilling to recover petroleum ether and separating to obtain crude fish oil, (d) mixing crude fish oil and hot water, constantly stirring at 90-95 degrees C, allowing to stand, precipitating, separating liquid layer, filtering mixture to remove impurities to obtain lower layer, transferring to distillation apparatus and distilling at 75-85 degrees C to remove raw materials in water to obtain standard feedstock oil, (e) mixing standard feedstock oil, methanol and solid base catalyst in a weight ratio of 100:70:3 in a reaction vessel, transferring into an ultrasonic oscillator and ultrasonic oscillating at 25-30 kHz for 1-2 hours, (f) transferring reaction product into a retort vessel, heating at 70-80 degrees C, distilling to remove methanol, filtering to remove impurities and separating to obtain crude biodiesel, (g) placing crude biodiesel in a 500 ml beaker, placing beaker in a high-speed mixer, heating under stirring at 60-70 degrees C, adding 5-10 g alkaline bleaching agent, increasing temperature to 95-105 degrees C for 35 minutes, decolorizing for 30-60 minutes and filtering.