The invention discloses an air heating device used for an alkali recovery furnace. An air outlet of an air blower is connected with an air pipe; the other end of the air pipe is connected with a cold air inlet of an air heater; a temperature sensor is arranged on the air pipe; a hot air outlet, a medium-pressure condensed water outlet, a low-pressure steam inlet and a low-pressure condensed water outlet are further formed in the air heater; the hot air outlet is connected with the air pipe; a pressure transmitter and a flow transmitter are arranged on the air pipe; a medium-pressure steam pipe is connected with a medium-pressure steam inlet of the air heater; a regulating valve is arranged on the medium-pressure steam pipe; a valve opening regulation execution mechanism is arranged on the regulating valve; a medium-pressure condensed water pipe is connected with the medium-pressure condensed water outlet of the air heater and a medium-pressure condensed water inlet of a medium-pressure condensed water collection groove; and low-pressure steam pipes are connected. The air heating device is simple in structure and low in running energy consumption; an alkali recovery production operation environment is effectively improved by water, the influence of hot steam on the environment is reduced, and the corrosion degree of water vapor to stress components of a factory building structure is reduced.