The invention relates to a method for obtaining polylactide polyol by a way of ring-opening polymerization of lactide with lactide and a polyol as direct raw materials. The method includes the following steps: A, lactide purification: a crude product lactide is purified, and lactide with the content of more than 99.5% and the optical purity of more than 99% is obtained; B, synthesis of polylactide polyol: the purified lactide and the polyol are added into a reaction kettle, then a catalyst is added according to a lactide weight ratio of 0.5/1000-1/1000 into the reaction kettle for polymerization, and polylactide polyol with the viscosity average molecular weight of 100-5000 is obtained, wherein the catalyst is a composite catalyst comprising one or more of zinc lactate, zinc oxide, zinc powder, diethyl zinc, tin lactate, tin oxide, tin dioxide, stannous oxide, stannous lactate, stannous octoate, stannous chloride, tin powder, propionic acid or tetrabutyl titanate. The method has simple process and easy operation, is suitable for industrialized production applications, and has no 'three wastes' emissions.