A top cover assembly for secondary battery, including: first and second electrode terminals; a top cover plate insulated from the first electrode terminal and electrically connected with the second electrode terminal; a contact piece attached to the top cover plate; and a thermo-deformable piece opposite to the contact piece, one end being electrically connected with the first electrode terminal, the other end being a free end; when a temperature at which the thermo-deformable piece deforms is not reached and internal pressure of the secondary battery exceeds a reference pressure, the contact piece deforms to be electrically connected with the thermo-deformable piece so that the first electrode terminal is electrically connected with the second electrode terminal, and when the temperature at which the thermo-deformable piece deforms is reached, the free end deforms away from the contact piece, and the thermo-deformable piece is kept insulated from the contact piece.