Abstract: The flying sawing machine is one of the key units of the straight welded pipe production line. For enhancement of length-cutting accuracy and consistent operation of the on-line flying sawer, a new PLC-DDC-D control system of flying sawer for the straight-welded pipe production line has been developed on the basis of studies of relevant flying sawer control systems developed both at home and abroad. Involved here are such aspects of the flying machine as operation process, design tips, length-measuring method and particularly configuration of the said control system and application of the full-digit direct current controller or the DDC to the design.