Abstract: Parameters of butt fusion welding of plastic pressure-pipe are different for varying pipe diameters and ambient conditions, and it is also affected by personal factor. Therefore,in this paper, four stages of the welding process were driven and the welding compression force was supplied by hydraulic system. In order to remove human element to improve the welding quality, the welding temperature, time and operation of hydraulic cylinder were controlled by 89C196 microprocessor, and welding parameters were selected and adjusted automatically according to pipe parameters and ambient conditions.