An operation mechanism of a circuit breaker includes: a tripping component; a left side plate; a right side plate; a latch; a half shaft; a lever; and a main shaft. The tripping component, the latch, the half shaft and the lever are mounted between the left side plate and the right side plate. The half shaft and the main shaft penetrate through the left side plate and the right side plate, and extend out of the left side plate and the right side plate. The lever includes a sheet metal bending piece. The sheet metal bending piece is bent to form a top wall and two side walls. The tripping component, the latch, the half shaft, the lever and the main shaft move in linkage. The tripping and the latch form a two-level latch. The operation mechanism of the circuit breaker is manual operation.