NOVELTY - Preparing biological diesel oil comprises: (a) preparing maggot oil: after drying and crushing the maggot, adding the solvent that is 1-10 folds of weight, leaching and extracting, filtering, after recycling solvent from the filtrate, obtaining the maggot oil; (b) ester exchanging: subjecting the maggot oil with low acidic value and methanol or ethanol to ester exchange reaction; (c) splitting phase: after finishing ester exchange, standing and layering the reactants; and (d) refining.    USE - The process is useful for preparing biological diesel oil (claimed).    ADVANTAGE - The process has wide raw material source, easy cultivation, and low production cost.    DETAILED DESCRIPTION - Preparing biological diesel oil comprises: (a) preparing maggot oil: after drying and crushing the maggot, adding the solvent that is 1-10 folds of weight, leaching and extracting for 1-48 hours at room temperature, filtering, after recycling solvent from the filtrate, obtaining the maggot oil with low acidic value of not greater than 2 or the maggot oil with high acidic value of greater than 2; where when the acidic value of the obtained maggot oil is greater than 2, pre-esterification is carried out; and when the acidic value of the obtained maggot oil is not greater than 2, the treatment conditions are: the mol ratio of the maggot oil with acidic value of greater than 2 to the methanol or ethanol is 1:6 to 1:13, and then adding acidic catalyst that is 0.5-5% of the weight of the maggot oil; where the reaction temperature is 40-90 degrees C and the reaction time is 0.5-4 hours; and the solvent is lipophilic organic solvent or mixture of lipophilic and hydrophilic organic solvents; (b) ester exchanging: subjecting the maggot oil with low acidic value and methanol or ethanol to ester exchange reaction; where the reaction conditions are: the mol ratio of the maggot oil with low acidic value to methanol or ethanol is 1:4 and 1:9, adding the alkaline catalyst that is 0.5-2.5% of the weight of maggot oil; where the reaction temperature is 40-90 degrees C and the reaction time is 10-60 minutes; (c) splitting phase: after finishing ester exchange, standing and layering the reactants; where the supernatant liquid is rough ester; and (d) refining: after washing the supernatant liquid of (c) by hot water, adding adsorbent that is 1-10% of the weight of the total composition, heating at 30-100 degrees C, agitating, filtering, obtaining filtrate that is biological diesel oil; or refining the supernatant liquid obtained by the reaction in (c) by using molecular distillation technology; where the vacuum pressure is 10-0.1 Pa; and the distilling temperature is 100-200 degrees C; and separating out biological diesel oil.    DESCRIPTION OF DRAWING(S) - The drawing shows a flow diagram of the process for preparing biological diesel oil (Drawing includes non-English language text).