Abstract: A robust PID controller design method was proposed, which was based on PID structured weight function optimization method with linear matrix inequality techniques. By combining static H_∞ loop shaping controller synthesis, a robust systematic PID iterative optimization method was given. A PID main controller of steam generator water level control system was designed by using this method. Simulation results show that the control system designed by the given method is of good robust stability and robust performance, and its synthetic control quality is better than the method of full order weight optimization (or PID structured weight optimization mentioned by this paper) combined with normal H_∞ controller synthesis.