The invention relates to the field of polyglycerol synthesis, in particular to polyglycerol-10 and a preparation method thereof. The preparation method of polyglycerol-10 comprises the following steps: (1) a crude polyglycerol product is prepared from glycerol and glycidol through a polymerization reaction in presence of an acid catalyst; (2) the polymerization reaction product is neutralized, a neutralization product is distilled by molecular distillation equipment, and the obtained heavy constituent is polyglycerol-10, wherein the heavy constituent condensing surface set by the molecular distillation equipment is at the temperature of 85 DEG C or higher, the light constituent condensing surface is at the temperature of 65-90 DEG C, and the heavy constituent condensing surface is higher than the light constituent condensing surface. With adoption of the method, the polyglycerol-10 product with higher purity is prepared with high yield by means of molecular distillation, and the method is beneficial to industrial production.