The invention discloses a waste heat boiler steam drum liquid level control system, and relates to the field of waste heat boilers. The waste heat boiler drum liquid level control system is installedat a waste heat boiler, and the waste heat boiler comprises a steam drum, a flue, a water feeding and regulating valve and a circulating pump, wherein front-end smelting equipment is installed at thefront end of the waste heat boiler, and water supply equipment and rear-end equipment are installed at the rear end of the waste heat boiler. The system comprises detecting components and a controller. By means of the waste heat boiler steam drum liquid level control system, an area control mode is adopted for the steam drum liquid level, the corrected liquid level value is not controlled througha single set value anymore, instead, a normal working area is additionally arranged on the basis of an existing set value, when the liquid level detection value is slightly changed, the water feedingand regulating valve is not controlled, and when the liquid level detection value is dramatically changed, the water feeding and regulating valve is controlled. In this way, control disordering causedby frequent regulating can be avoided; meanwhile, the using frequency of adjusting equipment is lowered, the service cycle of the equipment is prolonged, the control system is saved, and safe runningof the waste heat boiler is ensured.