A seal ring is provided for sealing a rotating shaft. The seal ring has an outer wall and an inner wall. The outer wall includes one or more external ribs, and the external ribs are disposed along a circumferential direction of the outer wall. The inner wall includes one or more seal contact parts extending inwards from the inner wall, and the seal contact parts are disposed along a circumferential direction of the inner wall. The seal ring is made of an elastic material.