In a method of manufacturing a thermoforming convex mold, the specification of a convex fixture is determined according to the curve shape of a thermoformed film sensor. The curve shape has a plane portion and a curve portion vertically downwardly extended from edges of the plane portion. The convex fixture has a base and a convex structure thereon. The height of each of the convex structure and the curve portion is in a range of 1 mm to 5 mm. The curvature radius of the curve corner between the top and the side wall of the convex structure is lower than 2 mm and higher than 0 mm. Next, the position of the side wall of the convex structure is uniformly shrunk inwardly by 0.4 mm to 0.6 mm, and the height of the convex structure is increased by 200% to 250%.