Flying splicer is a key component of web-fed offset presses for automatically replacing the exhausting web roll with a new one without stopping the machine. The composition and working principle of pneumatic controlling mechanism for operating the flying splicer is analyzed according to the processing requirements of automatic web alternation. By using the software FluidSim, the pneumatic sequential operation controlling circuitry with multi-cylinders for driving the flying splicer is designed, in which the air cylinders cooperate to accelerate the new reel to the circumferential velocity of the expiring web, paste the adhesive end of the new reel on the expiring web, and cut off the remaining piece of expired web. A system scheme and designing method of the PLC-based pneumatic controlling system suitable for automatic web roll change on high speed offset printing presses is brought out.