An automatically cleaned filter comprises a motor; a base above the motor; the base being formed with at least one filter seat, a water inlet, a water draining hole and an annular groove; at least one filter core installed on a respective one of the filter seat; the filtering material being formed on an outer side of the filter core; a cleaning unit installed on a center portion of the base; a bottom of the cleaning unit being connected to the spindle; a gear being installed at an upper side of the base and being engaged to the spindle; an upper cover combined to the base by using at least one supporting posts; a lower side of each filter core being installed with a gear; and the gear at the lower side of the filter core being engaged to the gear of the cleaning unit.