A low voltage circuit breaker with a modularized monopole belongs to the low voltage apparatus technical field, comprising a casing, a plurality of standard monopole circuit breaking arc-extinguishing device, an operation mechanism, and a tripping device. The standard monopole circuit breaking arc-extinguishing device comprises a left molding casing, a right molding casing, a movable and static contact element and a arc-extinguishing chute matched with the movable and static contact element. The invention is characterized in that the standard monopole circuit breaking arc-extinguishing devicealso includes a backing pressure tripping mechanism which is arranged on the casing wall of one of the left or right molding casings. The advantages are as follows: a rapid breaking effect is embodied; the monopole modules are independent; interphase short circuit is avoided because two phases share a commom voltage tripping; the critical trippping current among electrodes are consistent; sealingand structural strength are high enough that the conductivity of the phases is reduced; the backing pressure tripping mechanism is designed into a part along with the standard monopole circuit breaking arc-extinguishing device to make up the whole monopole module so as to reduce the phase difference.