The present application discloses a pressure relief mechanism, a battery cell and a battery. The pressure relief mechanism includes: a connecting mechanism including an aperture and a first boss, the first boss being connected to an inner wall of the aperture and extending toward an axis of the aperture; a pressure relief sheet for being actuated to release an internal pressure of the battery box when the internal pressure reaches a threshold and being arranged on a side of the first boss; a first protective sheet used to protect the pressure relief sheet and arranged on the other side of the first boss away from the pressure relief sheet; a compression ring arranged on a side of the first protective sheet away from the first boss; and a pressing structure connected to the connecting mechanism and being capable of being pressed toward the axis of the aperture.