The invention provides hydraulic systems for an oil filter with a forced oil filling function. By means of the hydraulic systems for the oil filter with the forced oil filling function, the problems that oil liquid in a hydraulic oil box flows too fast and is prone to generating bubbles, and high temperature and cavitation corrosion of working parts of the hydraulic systems are prone to being caused due to the hydraulic oil box is shared by different hydraulic systems of engineering vehicles are solved. The oil filter comprises a by-pass valve, an oil suction valve group, a safety valve group,an oil return filter core, an oil suction filter core, the hydraulic oil box and the hydraulic systems, wherein an oil suction valve and a safety valve are added in the oil return filter core, one oil suction filter core is connected in series at the same time, and oil suction and the oil return filter core are integrated; meanwhile, the safety valve with the forced oil filling function is added,the oil liquid of an oil return box is forced to fill an oil suction pipeline in priority, and the excess oil liquid returns to the oil box through the safety valve; and when oil return is insufficient, the oil liquid of the oil return box is all filled to the oil suction pipeline, and meanwhile, the oil suction valve is opened to help absorb oil from the hydraulic oil box to make up for the insufficient oil. The hydraulic systems for the oil filter with the forced oil filling function further have the advantages of simplifying oil box internal structures, reducing the cost of the filter cores and the like.