The invention discloses an RPT type water turbine main shaft sealing device, which comprises an adjusting cylinder, an end cover, an inner ring, an O-shaped sealing ring, a sealing ring and a rotating ring. The lower end of the cover, the end cover is set on the upper end of the inner ring, and the lower end of the inner ring is connected to the telescopic end of the adjusting cylinder; the upper end of the inner ring is provided with a water inlet hole, and the lower end of the inner ring is provided with an annular groove. A sealing ring is arranged in the groove, and the thickness of the sealing ring is greater than the depth of the annular groove, and a through hole is also provided in the circumferential direction of the sealing ring; The upper end surface is in contact, and the end cover, inner ring, O-ring, sealing ring, rotating ring and turbine main shaft end cover form an airtight sealing chamber; the RPT type hydraulic turbine main shaft sealing device designed in the present invention prevents pressure water from flowing from the main shaft of the water turbine and the water turbine The leakage between the main shaft end covers into the machine pit floods the water guide bearing and affects the operation.