A long-term stability test device for a ballasted track bed with a large ramp and a test method are disclosed, so as to perform an original proportional fatigue test on system stability of the ballasted track bed with the large ramp under the action of a long-term train load, so that a test result is more in line with engineering practice, correctness of a theoretical design method is effectivelyverified, and then optimization design of preliminary parameters is achieved. The test device includes a concrete base, an original proportion ballasted track bed system, a loading cross beam, a loading system, a sleeper displacement measuring device, and a track bed resistance test assembly; the concrete base is installed in a fatigue test loading pool, and the rear side of the fatigue test loading pool is provided with a lifting device for adjusting the top surface of the concrete base to a test slope degree; the original proportion ballasted track bed system is constructed on the top surface of the concrete base, and includes a ballasted track bed, sleepers, steel rails and fastener systems; the loading cross beam is fixed on the steel rails and are parallel to the sleepers, and the topsurface of the loading cross beam is a horizontal plane; the loading system acts on the top surface of the loading cross beam, and applies cyclic loading to the original proportion ballasted track bed system; the sleeper displacement measuring device comprises a measuring bracket and displacement sensors, the measuring bracket is fixedly mounted on the front end of the fatigue test loading pool,and the displacement sensors used for measuring displacement of the lowermost sleeper are disposed on the measuring bracket at equidistant intervals; and the track bed resistance test assembly is usedfor testing longitudinal resistance of the track bed or lateral resistance of the track bed.