The invention discloses a drum level control system comprising a main PID1 (Portion Integration Differentiation) control loop, an auxiliary PID2 control loop and an output correction module, wherein the main PID1 control loop takes a drum level as a target set value, the auxiliary PID2 control loop takes vapor output as a target set value, the main PID1 control loop and the auxiliary PID2 controlloop operate in parallel to calculate the opening value of a steam drum feed valve; the output correction module comprises a drum level change rate correction submodule and a water feed adjusting valve opening self learning submodule and is used for correcting the opening output of a water feed adjusting valve by tracing and judging the drum level fluctuation slope with the assistance of the opening self learning results of the water feed adjusting valve. The drum level control system can effectively maintain the stable drum level, and can response the condition of large water level fluctuation positively, so that a steam drum system can operate more safely and water level control become more stable. The drum level control system can be widely applied to drum level control in electric power, metallurgy and other industries.