The invention relates to a negative-pressure cleaning system used for a cooler of an auxiliary extruder vacuum system of a film production line. The negative-pressure cleaning system comprises the cooler, a filter, a first liquid level tank, a pump and a second liquid level tank; a liquid discharge tube of the cooler is connected to the filter through a first solenoid valve; the filter is connected to the first liquid level tank through a second solenoid valve; the first liquid level tank is connected to an inlet of the pump through a pump-in solenoid valve; an outlet path I of the pump is connected to the second liquid level tank through a pump-out solenoid valve; another outlet path I of the pump is connected to a liquid spray hole in a flange end cover through a liquid spray solenoid valve and a liquid spray flow regulating valve in sequence; the second liquid level tank communicates with an inner cavity of a cooler main body through a communication solenoid valve; and an outlet path I of the second liquid level tank is connected to the filter through an overflow solenoid valve, and another outlet path II of the second liquid level tank is connected to a liquid dropping and filling hole in the flange end cover through a dropping and filling solenoid valve and a dropping and filling flow regulating valve. The negative-pressure cleaning system can keep the cooling working surface of the cooler to be relatively clean, can keep cooling efficiency to be relatively stable, and has a self-cleaning function, so that manual labor amount is reduced.