An automatic water handling device of an air compressor includes a barrel and a pneumatic cylinder. The barrel has an interior space in which a division board formed with through holes is mounted to define a first chamber in which a desiccant agent is disposed and a second chamber. The barrel has a gas outlet opening connected with a gas accumulation tank. The second chamber has a gas inlet opening to receive compressed air. An electromagnetic valve is in connection with the second chamber and is connected to a timer for activation at predetermined time points by the timer to drive the pneumatic cylinder to open a control valve to drain off water removed from compressed air.