The invention discloses a method for synthesizing high-purity glycerin chlorohydrin under low pressure, which comprises the following steps: adding epoxy chloropropane and a solid superhigh acid catalyst into a hydrolysis kettle, starting stirring and heating, and introducing compressed air into the reaction system to keep the reaction pressure of the system at 0.2-0.35 MPa; dropwisely adding softened water into the epoxy chloropropane to perform hydrolysis reaction; (2) after the hydrolysis reaction finishes, carrying out solid-liquid separation on the hydrolysate and solid acid catalyst, sending the hydrolysate into a distillation kettle, and carrying out washing, drying and other simple treatment on the solid acid catalyst for reuse; and (3) carrying out vacuum distillation on the hydrolysate to remove water, and purifying with a scraper film evaporator to obtain the product glycerin chlorohydrin, wherein the vacuum degree of the vacuum distillation is 0.096-0.099 MPa, and the temperature is 90 DEG C. The purity of the synthesized product can reach 99.7% (GC) above, the impurity content is low, and the appearance is a colorless transparent thick liquid.