The invention relates to a hydraulic system component, and discloses a hydraulic oil tank and a return oil filter device of the hydraulic oil tank. The return filter device comprises a bucket body (1), a filter element (2) and a valve element (4). The bucket body (1) comprises a bottom wall (11) with an oil return port (13), and the valve element (4) comprises a connecting piece (42), a sealing piece (43) and a supporting piece (41). The filter element (2) can be axially moved between the first position and the second position. When the first element (2) is at the first position, the sealing piece (43) is separated from the bottom wall (11); and when the first element (2) is at the second position, the sealing piece (43) is connected to the bottom wall (11) and seals the oil return port (13). By means of the technical scheme, the oil return port can be sealed through the valve element when the filter element is pulled out to prevent unfiltered hydraulic oil from being drained through the oil return port, cleanliness of hydraulic oil in a hydraulic system can be ensured, and operation reliability of the hydraulic system can be improved.