A secondary battery, comprising an electrode assembly , a housing and a top cover assembly , wherein the housing has an accommodating chamber , the accommodating chamber having an opening, and the electrode assembly being accommodated in the accommodating chamber ; the electrode assembly comprises a plurality of electrode units , the plurality of electrode units being stacked in an axial direction (Z) of the accommodating chamber ; the top cover assembly comprises a top cover plate and an insulating member arranged on an inner side of the top cover plate , the top cover plate being connected to the housing , and the insulating member being located on a side of the electrode assembly in the axial direction (Z); and a first buffer gap (G1) is provided between the insulating member and the top cover plate ; wherein one side of the insulating member close to the top cover plate is provided with a first recess ; one side of the top cover plate close to the insulating member is provided with a fixing hole ; and the insulating member is provided with a connecting portion extending from a bottom wall of the first recess , and the connecting portion is inserted into the fixing hole of the top cover plate and is fixed to the top cover plate ; wherein the connecting portion comprises a first region (P1) and a second region (P2), the first region (P1) extending from a bottom wall of the first recess , the second region (P2) extending from an end of the first region (P1) away from the bottom wall and being inserted into the fixing hole , and a diameter of the first region (P1) is larger than a diameter of the second region (P2) and a diameter of the fixing hole . the housing has an accommodating chamber , the accommodating chamber having an opening, and the electrode assembly being accommodated in the accommodating chamber ; the electrode assembly comprises a plurality of electrode units , the plurality of electrode units being stacked in an axial direction (Z) of the accommodating chamber ; the top cover assembly comprises a top cover plate and an insulating member arranged on an inner side of the top cover plate , the top cover plate being connected to the housing , and the insulating member being located on a side of the electrode assembly in the axial direction (Z); and a first buffer gap (G1) is provided between the insulating member and the top cover plate ; wherein one side of the insulating member close to the top cover plate is provided with a first recess ; one side of the top cover plate close to the insulating member is provided with a fixing hole ; and the insulating member is provided with a connecting portion extending from a bottom wall of the first recess , and the connecting portion is inserted into the fixing hole of the top cover plate and is fixed to the top cover plate ; wherein the connecting portion comprises a first region (P1) and a second region (P2), the first region (P1) extending from a bottom wall of the first recess , the second region (P2) extending from an end of the first region (P1) away from the bottom wall and being inserted into the fixing hole , and a diameter of the first region (P1) is larger than a diameter of the second region (P2) and a diameter of the fixing hole . <EOS>