An operation mechanism of circuit breaker, comprising: a tripping component, a first side plate component, a second side plate component, a latch component, a half shaft component, a lever component and a main shaft component; the tripping component, the latch component and the lever component are mounted between the first side plate component and the second side plate component, the half shaft component and the main shaft component penetrate through the first side plate component and the second side plate component and extend out of the first side plate component and the second side plate component; the lever component comprises a sheet metal bending piece, the sheet metal bending piece being bent to form a top wall and two side walls; the tripping component, the latch component, the half shaft component, the lever component and the main shaft component move in linkage, wherein: the tripping component, the latch component and the half shaft component form a two-level latch; the tripping component is provided with a limiting device for limiting a stroke of the operation mechanism during a closing process and a free tripping process; the main shaft component is provided with a limiting device for limiting a stroke of the operation mechanism during an opening process; characterised in that: the tripping component comprises a tripping buckle, an upper connection rod and a lower connection rod; a rotation shaft of the tripping component is riveted to a first end of the tripping buckle and is arranged on the first side plate component and the second side plate component; a limiting hole is formed on the tripping buckle and a limiting pin is riveted in the limiting hole for limiting the stroke of the operation mechanism during a closing process and a free tripping process, a second end of the tripping buckle is hook shaped, a first inclined surface is formed on an inner side of the hook, and a second inclined surface is formed on an outer side of the hook and comprises an arc surface; the upper connection rod is riveted to the tripping buckle, and the lower connection rod is riveted to the upper connection rod; the latch component comprises a sheet metal piece, a bearing, a latch component spring and a rotation shaft; the sheet metal piece is installed on the rotation shaft of the latch component, the latch component spring is fit on the rotation shaft of the latch component, the latch component spring applies a spring force to the sheet metal piece, the bearing is installed on the sheet metal piece, the bearing is in contact with the second inclined surface at the second end of the tripping buckle, the latch component limits the tripping component; the half shaft component comprises a half shaft, two ends of the half shaft are installed on the first side plate component and the second side plate component respectively, the sheet metal piece is in contact with the half shaft component. the tripping component, the latch component and the half shaft component form a two-level latch; the tripping component is provided with a limiting device for limiting a stroke of the operation mechanism during a closing process and a free tripping process; the main shaft component is provided with a limiting device for limiting a stroke of the operation mechanism during an opening process; the tripping component comprises a tripping buckle, an upper connection rod and a lower connection rod; a rotation shaft of the tripping component is riveted to a first end of the tripping buckle and is arranged on the first side plate component and the second side plate component; a limiting hole is formed on the tripping buckle and a limiting pin is riveted in the limiting hole for limiting the stroke of the operation mechanism during a closing process and a free tripping process, a second end of the tripping buckle is hook shaped, a first inclined surface is formed on an inner side of the hook, and a second inclined surface is formed on an outer side of the hook and comprises an arc surface; the upper connection rod is riveted to the tripping buckle, and the lower connection rod is riveted to the upper connection rod; the latch component comprises a sheet metal piece, a bearing, a latch component spring and a rotation shaft; the sheet metal piece is installed on the rotation shaft of the latch component, the latch component spring is fit on the rotation shaft of the latch component, the latch component spring applies a spring force to the sheet metal piece, the bearing is installed on the sheet metal piece, the bearing is in contact with the second inclined surface at the second end of the tripping buckle, the latch component limits the tripping component; the half shaft component comprises a half shaft, two ends of the half shaft are installed on the first side plate component and the second side plate component respectively, the sheet metal piece is in contact with the half shaft component.