Abstract: In this article, the computer control system of the large scale flashing butt welding was introduced in the aspects of the makeup and its realization. The computer control system was adopted in stead of the traditional PLC method. In this system, the large scale SCR was controlled via the computer and the power voltage compensation. The protection of the solo phase SCR connection and the welding process as well as the control of the outer characteristic of the machine were realized by the voltage and current close-loop feedback. the flashing curve was finished by using the ratio valve, which can also be used in the new workpiece technology debuggging. The parameters of the control system were collectecd by photoelectrical seclusion to avoid the disturbing of the electromagnetism in welding. Therefore, this system achieved the perfect effect in control and protection.