The invention relates to special production equipment for plastic bags for liquid, in particular to a special heat sealing machine for plastic bags for liquid. Circular material openings are welded on plastic films and material nozzles by the aid of heat sealing process, and the special heat sealing machine comprises a heater and an electric heating wire mounted in the heater. The special heat sealing machine is characterized in that the heater consists of a center shaft, a pressure plate and a base, the pressure plate is mounted on the center shaft, a plurality of positioning rods are circumferentially uniformly distributed on the pressure plate and inserted in sleeves, a buffer spring is arranged between each positioning rod and the corresponding sleeve, the lower end of each sleeve is fixedly connected with a heating ring, the heating rings are positioned between the pressure plate and the base, and a driving device capable of pushing the pressure plate to move axially is disposed on the center shaft. The special heat sealing machine for plastic bags for liquid is specially used for welding the circular material nozzles on the plastic bags for liquid, and is simple in structure, high in efficiency and fine in heat sealing quality.