The invention discloses a volume-adjustable isolation oil cylinder, and belongs to the technical field of hydraulic systems. The oil cylinder comprises a cylinder bottom, a first in-place induction mechanism, a second in-place induction mechanism, a supporting sleeve, a second spring, a cylinder barrel, a piston, a volume adjusting assembly and an end cover; the cylinder bottom is arranged at oneend of the cylinder barrel, the volume adjusting assembly and the end cover are arranged at the other end of the cylinder barrel, the supporting sleeve is located in the cylinder barrel, the piston isarranged in the cylinder barrel, the supporting sleeve is sleeved with the second spring, the first in-place induction mechanism is arranged on the cylinder bottom and in the supporting sleeve, whenthe piston moves to be in place in the cylinder bottom direction, the first in-place induction mechanism is triggered, the second in-place induction mechanism is arranged on the volume adjusting assembly and the piston, and when the piston moves to be in place in the direction of the end cover, the second in-place induction mechanism is triggered; according to the oil cylinder, hydraulic oil in ahydraulic pipeline of an in-cabin hydraulic system and hydraulic oil in a hydraulic pipeline of an out-cabin hydraulic execution part are isolated, and the exterior liquid is prevented from being brought into a hydraulic oil tank of the hydraulic system.