The invention relates to a method for making biological diesel oil, in particular to a method for making biological diesel oil by seeds and fruit of plants. The making steps of the invention are as follows: the seeds and fruit of the plants are separated, dried and crushed and put in a reaction kettle provided with a
cutting and blending device (the rotary speed is more than 300rev / m) and added with bridle chain alcohols and
fatty acid methyl esters, and the mixture undergoes high speed
cutting and stirring at the
room temperature for 1 to 4 hours to form uniform suspension liquid, and the suspension liquid is added with alkalescent materials and undergoes high speed stirring for 1 to 4 hours; KOH or NaOH is dissolved in methyl alcohols to prepare the KOH or NaOH
methanol solution with
mass percentage concentration between 8 and 10 percent, which is used as catalyst; the suspension liquid is added with the catalyst and undergoes the back flow reaction for 0.5 to 4 hours; after the reaction, reactants are cooled down to the temperature of 40 DEG C and then undergo pressure
filtration to obtain separated filtrate, and filter cakes are used for other purposes; the separated filtrate undergoes the standing separation to remove side products such as glycerin, etc. on the lower layer, and coarse products of biological diesel oil are obtained; the coarse products of biological diesel oil undergo normal pressure
distillation to recover excessive bridle chain alcohols and undergo molecular
distillation to obtain the qualified biological diesel oil. The method of the invention has the advantages of simple production process, high
utilization rate of vegetable fat, low manufacturing cost and good economical efficiency of process, and has a good prospect for large-scale popularization and application.