The invention discloses an automatic drainage anchor rope system for slope protection and a construction method thereof. The automatic drainage anchor rope system has anchor rope reinforcement and drilled hole drainage functions at the same time, the effect that one hole has multiple purposes is achieved, and the slope safety coefficient is greatly increased under the same construction cost. The automatic drainage anchor rope system comprises a drilled hole, a steel strand, an isolating pipe, a water-pervious pipe, a water swelling rubber water stopping ring, a drainage pipe, a protective pipe, cement mortar and an outer anchor head; underground water infiltrates into the gap between the water-pervious pipe and the isolating pipe through a drainage section, so that the water pressure in the gap is increased, when the water head of a water inlet of the drainage pipe is higher than the elevation of an opening of the drilled hole due to the fact that the water level of the underground water rises, the underground water in the gap naturally flows out from the drainage pipe, syphonage is naturally started, and the underground water in a slope is discharged. The drainage work process is conducted circularly along with falling of rain, the pump drainage effect of the drainage pipe changes periodically and circularly, long-time efficient real-time continuous drainage of the system is achieved, and the drainage governance problem of large-scale landslide is solved.