The problem of the water level control of the steam generator makes the plant more vulnerable to high and low level trips. Particularly, the swell and shrink phenomena and the flow errors at low power levels make the level control of steam generators difficult. At this work, the flow errors are regarded as the time-varying parameters and estimated by the parameter estimation algorithm of the least square method. Using the estimated flowrates, the unmeasurable level quantity due to the mass capacity effect is estimated and the level quantity is used in order to calculate the control input. Under the assumed flow errors, the proposed controller shows good performances and robustness.