Objective To improve the wear resistance and corrosion resistance performance of piston rods, and reduce the manual participation in processing system. Methods According to the process requirements of the surface treatment on nine-meter plunger rods by adopting oxygen-acetylene flame spray welding, the automatic control system was developed through selecting the control method and controller. With PLC automatic control as the core, the self-fluxing alloy powder flame spray welding was finished through the coordination among the movement and rotation of the plunger rod, the rise and fall of cylinders, the oxygen-acety-lene flame spraying device and limit switches, and the touch screen was applied to realize visual monitoring of the surface treatment process and parameter settings. Finally, the automatic control system was evaluated based on the actual spraying result. Results Practical application proved that the system was stable and reliable, the parameter setting was flexible, and the automatic control of surface treatment process on plunger rods was realized. The workpiece prepared showed high uniformity in surface coating, and had high quality and good performance. Conclusion The system was applicable to different lengths of plunger rods shorter than 9 meters and spray welding process with different coating materials, greatly improving the production efficiency, and could be generalized to relevant fields.