The invention discloses a finishing turning technology for a piston rod of a marine diesel. The piston rod of a main engine belongs to slender shaft parts and has high hardness after quenching. Grinding is the most frequently used processing method for the piston rod. However, the grinding efficiency is low, the cost is high, the energy consumption is large, and grinding liquid employed for grinding is large in pollution to the environment. According to years of practical experience of our company for processing piston rods, and by learning from domestic and overseas advanced technologies and processing methods, we discover that replacing grinding with finish turning is an important way of improving the piston rod processing efficiency, namely, a superhard cutting workpiece is used for replacing a grinding workpiece. The technology is high in processing efficiency and low in energy consumption. Complex parts can be easily cut and cuttings are easily recycled, so that environment protection is facilitated. Therefore, replacing grinding with finish turning for quenched piston processing has a good prospect in the aspect of remarkably reducing cost and improving efficiency.