Influences of the bias states of saturable absorbers on bistable InGaAsP multi-quantum-well(MQW) common cavity tandem section(CCTS) semiconductor lasers were investigated experimentally and theoretically. The experiment demonstrated that the bistability characteristic of P-I curves can be more significant with increasing reversed bias voltage in the saturable absorber(SA), and a negative differential resistance phenomenon was found in V-I curves. When the voltage was -3 V, the hysteresis width was broadened to 13.5 mA, with the on-off ratio up to 21: 1. The theoretical analysis proves that higher passive voltage in SA and shorter carrier escape time can result in better bistability. The maximum on-off ratio as high as 107: 1 promises that a common cavity two-section laser can be switching between the two-steady state.