NOVELTY - Purified trench oil, short-chain alcohol gas, and acidic catalyst are pre-esterified, to obtain mixture of fatty-acid short-chain ester, oil, glycerol, and water. Alkali catalyst and alcohol are added to the liquid mixture, and alcohol is reacted with oil and catalyst to obtain ester and glycerol. Ester is separated from glycerol. Ester and oil having smaller specific gravity are supplied to another hypergravity reactor. After glycerol is separated from the liquid mixture, the ester and mixture of other components are purified.    USE - Method of using trench oil as raw oil to produce biodiesel oil.    ADVANTAGE - The method enables quick, continuous and economical manufacture of biodiesel oil of high quality, using trench oil as raw oil, consuming less energy.    DETAILED DESCRIPTION - Purified trench oil is supplied to an esterifier through a nozzle. Short-chain alcohol gas (20-40%) and acidic catalyst (0.15-0.3%) are added and heated to 60-75 degrees C. The contents are pre-esterified, to obtain a liquid mixture of fatty-acid short-chain ester, oil, glycerol, and water. The liquid mixture is returned to the esterifier through the nozzle by the action of a continuous compression pump, and the unreacted short-chain ester in the esterifier and water generated by the reaction are discharged out from an outlet and supplied to a fractionator for moisture separation. The short-chain alcohol gas is recycled to the esterifier for further use. When the acidity of the material in the esterifier is less than 1 mgKOH/g, a portion of liquid mixture is pumped into a hypergravity reactor through the liquid outlet of the esterifier. The esterifier is replenished with equal amount of oil, short-chain alcohol, and acidic catalyst for balancing and carrying out continuous reaction. The additional amount of short-chain alcohol is 20-30% of oil and the additional amount of acidic catalyst is 0.15-0.3% of oil. The short-chain alcohol is methanol, ethanol, propanol or butanol. The acidic catalyst is sulfuric acid, phosphoric acid, methyl benzenesulfonic acid, alkyl benzenesulfonic acid, methyl ester bisulfate, or strong acidic ion-exchange resin. An alkali catalyst (0.15-0.5% of trench oil) is added to the liquid mixture discharged from the outlet. The mixture is axially supplied to a rotor having a rotating speed of 600-900 rpm from the liquid nozzle of hypergravity reactor. By the action of rotor, the liquid is moved in the centrifugal direction. Simultaneously, short-chain alcohol gas (20-30% of tunnel oil) is added on the shell inlet of the hypergravity reactor at normal pressure and reactant temperature, the alcohol reacts with oil and alkali catalyst moving at high speed under the action of rotor, to obtain fatty-acid short-chain ester and glycerol. The resultant product is discharged from the outlet of hypergravity reactor and supplied to a dish segregator. The ester is separated from glycerol by the action of high-speed rotor of the dish segregator at a rotating speed of 1000-7000 rpm, and glycerol having higher specific gravity is discharged from the bottom of the segregator. Ester and oil having smaller specific gravity are discharged from the segregator and supplied to hypergravity reactor of stage (II). Equal proportion of alcohol and alkali catalyst as the weight of oil is replenished. After glycerol is separated from the liquid mixture discharged from the outlet of hypergravity reactor, the ester and mixture of other components are returned for purification. The alkali catalyst is potassium hydroxide. The mixture containing ester, unreacted alcohol, and oil is pumped into an evaporator and heated to 70-100 degrees C under normal pressure. The short-chain alcohol is recycled. The ester is washed with salt water (0.2-1 time its own weight), decompressed to 10-20 kPa, and dehydrated to obtain final product of mixed fatty-acid short-chain ester of required quality.