Method for preparing vinyl chloride-based polymer

A method for preparing a vinyl chloride-based polymer, the method comprising:

• a step of injecting an ionizable normal salt and polymerizing a vinyl chloride monomer in the presence of one or more emulsifiers and a polymerization initiator,
• wherein the ionizable normal salt comprises a carbonate metal salt or a sulfite metal salt, wherein the ionizable normal salt is continuously injected in an amount of 70 to 1200 ppm based on the total weight of the vinyl chloride monomer when a polymerization conversion rate is in a range of 0% to 20%,
• wherein when the polymerization conversion rate being 0% is a point where polymerization reaction begins immediately after initiating the polymerization of the vinyl chloride monomer,
• wherein the polymerization is performed by the steps comprising:
• injecting supplementary materials comprising an emulsifier and water to a reactor;
• applying vacuum to the reactor and then injecting the polymerization initiator and the vinyl chloride monomer;
• and
• continuously injecting the ionizable normal salt to the reactor after the inner temperature of the reactor reaches 30 to 70° C.