The invention relates to the technical field of die steel surface modification treatment, in particular to a laser remelting method for ultrasonic spraying of a WC-12Co coating on the surface of H13 hot work die steel. The surface of the H13 hot work die steel is polished, cleaned and subjected to sand blasting. The laser remelting method is characterized in that the WC-12Co coating is sprayed to the surface of the H13 hot work die steel subjected to sand blasting through an ultrasonic spraying method, after heat preservation and cooling to the room temperature, laser remelting is used for remelting the WC-12Co coating and the surface of the H13 hot work die steel to achieve metallurgical bonding; and the structure property of the cooled coating is enhanced, and abrasion resistance of the coating is improved. The bonding strength of the coating and the base material is improved, and the service life of a mold is prolonged.