The invention relates to a method for reducing the moisture content of 1,3-propane sultone. The method comprises the following steps: preparing1,3-propane sultone which can be applied to a lithium ion secondary battery, weighing a crude 1,3-propane sultone product, subsequently adding a dewatering agent and water into the crude 1,3-propane sultone according to a certain mass ratio and putting into a reaction kettle together, and sealing and heating for more than half an hour at normal pressure; (2) putting the crude 1,3-propane sultone product obtained in the step (1) into a rectifying tower for reduced pressure rectification, namely, performing reduced pressure rectification when the pressure is lower than 10mmHg, the temperature of the reaction kettle is controlled to be 140-160 DEG C and the temperature of the tower top is 100-120 DEG C, thereby obtaining the 1,3-propane sultone of which the moisture content is within 100ppm, the acidity is lower than 100ppm and the purity is greater than 99.98%. The method provided by the invention is simple and convenient to operate, low-temperature heating is kept in the operation process, a product and a raw material are effectively prevented from being carbonized and deteriorated, and moreover an obtained product is low in moisture content and high in purity.