Belonging to the technical field of byproduct industrial salt treatment, the invention relates to a melting furnace for byproduct industrial salt treatment and a treatment method. The melting furnace includes a furnace cavity body formed by a plurality of surrounding furnace wall surfaces, the furnace cavity body has an upper part defined as a heating cavity and a lower part defined as a smelting cavity, the furnace wall of the heating cavity is equipped with several flame nozzles, and the smelting cavity is internally equipped with at least two weirs higher than the bottom surface of the smelting cavity. The invention also discloses a method of treating byproduct industrial salt with the melting furnace. The melting furnace and treatment method provided by the invention greatly improve the treatment effect of the byproduct industrial salt and ensure the quality of a final product.