This invention relates to a correctional method of water level in the steam drum based on the temperature and pressure that belongs to the heat process control field including the following steps: the temperature difference DeltaT is linear to the water supply flow increment in small range, DeltaQ=-kDeltaT, theDeltaQ is used as the feedforward value in the main circuit of the cascade control of the water level in the steam drum, to eliminate the adverse effect of 'false water level' on the water supply control. When the load increases,DeltaQ>0, and the steam drum working condition is nearly stable, the correctional value is 0; when the load decreases, the controlled water supply is suppressed, DeltaQ<0; when the water flow increases, the temperature T of the steam drum decreases and the water supply flow increment DeltaQ<0; when the water supply flow is nearly constant, the correctional value is 0; when the water supply flow decreases, the controlled supply flow increases, DeltaQ>0. This method introduces the effect of steam drum pressure and water temperature on the steam bubble in the steam drum water to correct the water level control, which suppresses the overshoot phenomenon and ensures the steady operation of the boiler.