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. <EOS>