The utility model relates to a welding device for plastic doors and windows, which can weld doors and windows of which the inner cavity is provided with a reinforced steel angle core. On the basis of the original device, a heating plate of the utility model is divided into two blocks, the height of the joint line of the left side and the height of the joint line of the right side are malposed, which is favorable for improving the welding quality. The position of the joint line of the heating plate is provided with a trapezoidal opening which is favorable for the self-positioning of a welding plate. The center of the trapezoidal opening is provided with a hole, and a steel angle core can exactly pass through the hole, so that the outer layer of plastic profile can be smoothly heated to a fusion jointing temperature and the two heating plates can recede towards two opposite directions after the heating is completed. At the moment, a tong-shaped plate presses the profile, and a weld crater of the plastic profile can be quickly closed along one side of the reinforced steel angle core. The melting plastic can be self-melted to complete the welding.