The invention relates to a mechanism with a flexible sub switch buffering anti-rebound device on a low-voltage circuit breaker. The low-voltage circuit breaker comprises left and right fixed plates, amain shaft arranged between the two fixed plates and is used for forming a transmission mechanism, and a contact mechanism which is arranged between the fixed plates. The mechanism with a flexible sub switch buffering anti-rebound device comprises a bracket, an oil cup, a cup cap, a piston, crank arms and a roller. The bracket is fixed on the fixed plates, the oil cup is fixed on the bracket andis filled with oil, the piston is arranged in the oil cup, an upper end of the piston is connected to the cup cap, the crank arms are connected to the main shaft, the roller is connected between the two crank arms, and the roller is located directly above the cup cap. When the circuit breaker is switched on, the roller is not in contact with the cup cap, when the circuit breaker is switched off, the main shaft rotates to drive the roller to move to press the cup cap down, the cup cap drives the piston to move downward, and the oil in the oil cup is compressed. When the circuit breaker is quickly switched off and an opening distance is small, the rebound of the circuit breaker in switch-off can be reduced by the mechanism of the invention.