Ultrasonic sealing machine is a kind of ultrasonic welding machine, which uses ultrasonic energy concentrator to act on the sealing part of the packaging container to seal the packaging container. The ultrasonic energy is transmitted to the welding area through the upper weldment. Because of the high sound resistance at the welding area, i.e. the interface between the two welds, local high temperature will occur. And because of the poor thermal conductivity of the plastic, it can not be distributed in time for a while, and it is gathered in the welding area, resulting in the rapid melting of the contact surface of the two plastics, and after adding a certain pressure, it will be fused into one. When the ultrasonic stops working, let the pressure continue for several seconds to solidify and form a solid molecular chain to achieve the purpose of welding. The welding strength can be close to the strength of raw materials.