The present disclosure provides a cap plate and a secondary battery. The cap plate includes a main portion and a first protruding portion. The main portion includes a first exterior surface, a second exterior surface and a third exterior surface, the third exterior surface is a curved surface. The first protruding portion includes a fourth exterior surface extending downwardly from a bottom end of the third exterior surface, the fourth exterior surface is inclined inwardly relative to the third exterior surface. The secondary battery comprises the cap plate and a case. The case includes an opening; the cap plate is provided to the opening, the main portion is fixed to an inner wall of the case. The first protruding portion is received in the case, and a gap is provided between the fourth exterior surface and the inner wall, a dimension of the gap increases gradually along a downward direction.