Abstract: In view of difficulty of PID parameters tuning for feedforward and feed-back three elements level control system of U-type steam generator, and high requirement of control system robustness, PID parameters tuning for primary controller was given based on H_∞ loop shaping method. Comparison simulations were made between PID parameters set by traditional methods and set by H_∞loop shaping approach. Simulation results show that the control system tuned by this method has good control performance and robust stability.