A top cover assembly of a secondary battery, characterized in that the top cover assembly comprises: a top cover plate; and a valve sleeve, wherein the top cover plate comprises an accommodation groove and a valve part protruding upward from a bottom wall of the accommodation groove, and the valve part is provided with at least one gas exhaust hole that communicates with an interior of the secondary battery; and the valve sleeve is accommodated in the accommodation groove and covers the valve part, a gas exhaust passage that communicates with outside is disposed between the valve sleeve and the valve part, and the gas exhaust passage communicates with the at least one gas exhaust hole, the valve part is provided with a first groove, the first groove opening towards the valve sleeve and communicating with the at least one gas exhaust hole, and a lower surface of the top cover plate is provided with a second groove, and the at least one gas exhaust hole is located in an area surrounded by an outline of the second groove; the valve sleeve is made of a deformable material, the valve sleeve is configured to deform under a force applied by gas exhausted from the at least one gas exhaust hole, so as to form the gas exhaust passage between the valve sleeve and the valve part, and the valve sleeve is configured to be in tight coupling with the valve part, when the force applied by the gas is smaller than a force under which the valve sleeve begins to deform, and the top cover further comprises a valve cover connected to the top cover plate, wherein the valve cover is in position-limit fit with the valve sleeve in a height direction of the secondary battery. a top cover plate; and a valve sleeve, wherein the top cover plate comprises an accommodation groove and a valve part protruding upward from a bottom wall of the accommodation groove, and the valve part is provided with at least one gas exhaust hole that communicates with an interior of the secondary battery; and the valve sleeve is accommodated in the accommodation groove and covers the valve part, a gas exhaust passage that communicates with outside is disposed between the valve sleeve and the valve part, and the gas exhaust passage communicates with the at least one gas exhaust hole, the valve part is provided with a first groove, the first groove opening towards the valve sleeve and communicating with the at least one gas exhaust hole, and a lower surface of the top cover plate is provided with a second groove, and the at least one gas exhaust hole is located in an area surrounded by an outline of the second groove; the valve sleeve is made of a deformable material, the valve sleeve is configured to deform under a force applied by gas exhausted from the at least one gas exhaust hole, so as to form the gas exhaust passage between the valve sleeve and the valve part, and the valve sleeve is configured to be in tight coupling with the valve part, when the force applied by the gas is smaller than a force under which the valve sleeve begins to deform, and the top cover further comprises a valve cover connected to the top cover plate, wherein the valve cover is in position-limit fit with the valve sleeve in a height direction of the secondary battery.