The invention discloses a preparation method of polylactide polyol. The preparation method comprises steps as follows: with an organic compound as a catalyst and a polyol compound as a chain transfer agent, lactide is catalyzed to be subjected to a polymerization reaction, and polylactide polyol is obtained. The adopted organic compound catalyst has the characteristics of being non-toxic and efficient, the catalytic activity is higher than 1 kg/g, no toxic byproducts are generated in the reaction process, steps are simple and easy to implement, and the preparation method is environment-friendly; the molecular weight of the obtained polylactide polyol is 500 g/mol-10,000 g/mol, the molecular weight distribution is 1.1-1.5, the biodegradability is good, and the obtained polylactide polyol can meet the application requirements and used for synthesis of biodegradable materials.