A method for forming a cover of an umbrella including preparing several pieces of cloth, clamping the perimeters of the cloth and pulling the cloth downward against a lower mold having a convex shape, heating the lower mold in order to soften the cloth, moving an upper mold downward to clamp the cloth, heating the lower mold again in order to further increase the temperature of the lower mold so that the cloth can be hot-pressed, cooling the lower mold, removing the cloth, and cutting the perimeter of the cloth so as to form the cover of the umbrella.