A fusion welding isolation mechanism for an operation mechanism of a circuit breaker, wherein: the operation mechanism of circuit breaker comprises a lever component and a main shaft component; the main shaft component comprises: a main shaft; a plurality of cantilevers arranged on the main shaft; and main shaft limiting pieces (239, 240) arranged on the main shaft; the lever component comprises: a bent sheet metal bending piece including a top wall and two side walls; a lever component spring mounted on the sheet metal bending piece and surrounded by the sheet metal bending piece; and an operation handle for driving the lever component in rotation; the fusion welding isolation mechanism comprises isolation devices configured to be arranged on the lever component and the main shaft component for preventing the operation handle from an opening operation when a moving contact is subject to fusion welding, characterized in that the isolation devices comprise: a shallow hook shaped extension part formed at an end of the bottom of each of the two side walls of the sheet metal bending piece; and limiting blocks provided on the main shaft limiting pieces (239, 240) and matching the shallow hook shaped extension parts; and wherein, when a moving contact is subjected to fusion welding, the main shaft component in linkage with the moving contact is locked at a closing position and is not able to rotate, and when the lever component rotates towards an opening direction under an external force, each limiting block is in contact with the corresponding shallow hook shaped extension portion, so that the lever component is not able to reach an opening position. the operation mechanism of circuit breaker comprises a lever component and a main shaft component; the main shaft component comprises: a main shaft; a plurality of cantilevers arranged on the main shaft; and main shaft limiting pieces (239, 240) arranged on the main shaft; a main shaft; a plurality of cantilevers arranged on the main shaft; and main shaft limiting pieces (239, 240) arranged on the main shaft; the lever component comprises: a bent sheet metal bending piece including a top wall and two side walls; a lever component spring mounted on the sheet metal bending piece and surrounded by the sheet metal bending piece; and an operation handle for driving the lever component in rotation; a bent sheet metal bending piece including a top wall and two side walls; a lever component spring mounted on the sheet metal bending piece and surrounded by the sheet metal bending piece; and an operation handle for driving the lever component in rotation; the fusion welding isolation mechanism comprises isolation devices configured to be arranged on the lever component and the main shaft component for preventing the operation handle from an opening operation when a moving contact is subject to fusion welding, characterized in that the isolation devices comprise: a shallow hook shaped extension part formed at an end of the bottom of each of the two side walls of the sheet metal bending piece; and limiting blocks provided on the main shaft limiting pieces (239, 240) and matching the shallow hook shaped extension parts; and wherein, when a moving contact is subjected to fusion welding, the main shaft component in linkage with the moving contact is locked at a closing position and is not able to rotate, and when the lever component rotates towards an opening direction under an external force, each limiting block is in contact with the corresponding shallow hook shaped extension portion, so that the lever component is not able to reach an opening position. a shallow hook shaped extension part formed at an end of the bottom of each of the two side walls of the sheet metal bending piece; and limiting blocks provided on the main shaft limiting pieces (239, 240) and matching the shallow hook shaped extension parts; and wherein, when a moving contact is subjected to fusion welding, the main shaft component in linkage with the moving contact is locked at a closing position and is not able to rotate, and when the lever component rotates towards an opening direction under an external force, each limiting block is in contact with the corresponding shallow hook shaped extension portion, so that the lever component is not able to reach an opening position.