The invention provides a mechanical cleaning device for a product oil tank. The mechanical cleaning device comprises a to-be-cleaned oil tank, a water chamber, and a washing pump. The mechanical cleaning device for the product oil tank is characterized in that the to-be-cleaned oil tank is orderly communicated with a filter and a vacuum suction tank, and the vacuum suction tank is divided into three routes, wherein the first route is orderly communicated with the washing pump, at least one ejector, and the to-be-cleaned oil tank; the second route is communicated with a recovery pump and divided into two routes, wherein one route is orderly communicated with an ultrafilter and a recovered oil tank, and the other route is communicated with an oil-water separation tank by a cyclone separator; and the third route is orderly communicated with a vacuum pump and the oil-water separation tank; an upper pipe of the oil-water separation tank is divided into two routes, wherein one route is connected with an evacuation pipe through a flame arrester, and the other route is connected with the to-be-cleaned oil tank; a lower pipe of the oil-water separation tank is divided into two routes through a valve and a membrane pump, wherein one route is communicated with the recovered oil tank through the ultrafilter, and the other route is communicated with an air compressor; and a water pipe of the oil-water separation tank is divided into two routes through a valve, wherein one route is communicated with the cleaning pump, and the other route is communicated with the oil-water separation tank by the cyclone separator. The mechanical cleaning device can efficiently, safely and conveniently clean the to-be-cleaned oil tank.