The present invention relates to a preparation method for a biological polybasic alcohol by using of an aleurites fordii. The preparation method is as follows: an alcohol-decomposing agent is added into the aleurites fordii to make the alcohol-decomposing reaction in the catalyzing environment to create a mixing ester of fatty acid; and then an epoxidizing agent is added into the mixing ester of fatty acid to make the epoxidizing reaction in the catalyzing environment to create a mixing epoxidizing ester of fatty acid; the mixing epoxidizing ester of fatty acid takes the opening reaction of epoxidizing key with an opening agent to create a mixing hydroxylic ester of fatty acid, i.e. a biological polybasic alcohol. The biological polybasic alcohol takes the addition reaction with an oxidation alkene in the catalyzing environment to create a biological polybasic alcohol with much higher molar weight. The preparation technics and operation of the present invention are more convenient; the adjustability for the product function is much better with much better performance. The aleurites fordii materials used in the present invention is a reproducible materials; so the cost is much lower and the material is abundant, which can replace the petrifaction polyether glycol to prepare the polyurethane foam plastic so that the dependence to the polyurethane product decreases.