An iron-core coil assembly is provided, which includes a substrate, a plurality of U-shaped wires, a first pin, a second pin, and an iron-core device. The substrate has a groove divided into a winding area and a non-winding area. The plurality of U-shaped wires is disposed in the winding area at a space from each other, and each U-shaped wire has an opening and a recess. The first pin and the second pin are respectively arranged at two ends of the opening, and the recess is located in the groove. The iron-core device is disposed in the groove, and passes through the recess of each U-shaped wire.