The invention discloses an air filter device of a composite cooler of a haulage motor. An air inlet of a shell is connected with an air outlet of a ventilator, an air outlet of the shell is connected with an air inlet of an oil-water cooler; a filter element is an electrostatic metal plate in a crossed and staggered grid plate structure, and is connected with a direct current supply and insulated with the shell; a dust collecting box is of a funnel structure with a door at one side, and is arranged at the downstream of the electrostatic metal plate. Tiny objects in airflow are adsorbed on the electrostatic metal plate by static electricity and are deposited in a funnel deposition box along a diversion trench under dual action of wind power and gravity of the tiny objects due to the included angle between the electrostatic metal plate and the axis of an air flue inside the shell and the crossed and staggered grid plate group structure, and thus the problems of dust retention and influence on heat dissipation of a cooling plate are effectively solved. At daily time, only the funnel-type dust collecting box with the door at the side needs to be cleaned, and under extreme conditions, the drawer-type electrostatic metal plate also can be easily taken down by opening the side door of the shell to clean. Thus, the cooling effect is greatly improved.