The invention discloses a method and device for preventing oil seepage and oil leakage of a hydraulic system. A filter device is arranged at the outer portion of an oil tank of the hydraulic system and comprises a hydraulic pump, a filtering assembly, an oil taking pipeline and an oil returning pipeline. Hydraulic oil in the hydraulic system is sucked from the oil tank of the hydraulic system through the hydraulic pump, and after being filtered through the filtering assembly, the hydraulic oil is discharged to the oil tank through the oil returning pipeline. According to the method and device for preventing oil seepage and oil leakage of the hydraulic system, the filter system is arranged outside the hydraulic system, circular filtering can be conducted without shutdown so as to improve the cleanliness of an oil product in the hydraulic system, and the phenomenon that due to the fact that a sealing piece is polluted and corroded by the hydraulic oil and fails, oil seeps and leaks is reduced.