Steam generator water level control incorporates the system that controls the speed of the main water feed pump and the one that controls the degree to which the main water feed valve is open. Although these two control systems are set independently, they have a reciprocal influence. A key problem is that, in the actuator for the regulation of the two systems, the regulated variables tend to oscillate with a relatively large amplitude even under stable conditions. In this paper, a pervasive regulating resonance phenomenon is inspected and analyzed by means of simulating the real working conditions. And using a mathematical model of the main water feed flow, it reveals that the two factors which directly cause the regulation resonance phenomenon are the frequency characteristics of the control system and the phase difference. On the basis of this, three potential optimization schemes have been proposed: the optimization of the regulation parameters; changing the phase difference; and setting a regulation dead-band which can improve the stability of the control system.