The major difficulties encountered in controlling the steam generator water level swell and shrinkage are analyzed. A mathematical model based on the amount of steam generated by depres-surization during the periodic steam dump is used to predict the level changes. When the existing proportional integral controller is applied to the negative of these predicted level changes and the output is added to the controller output for the normal level error, it is found that the water level does not go down below the lower limit or up beyond the higher limit. This control algorithm is tested on a model steam generator, and the results show it is capable of handling the difficulties in the control of the level swell and shrinkage.