The invention relates to a low-voltage circuit breaker with a residual current trip device. A plurality of circuit breaker poles which are arranged in parallel and the residual current trip device are arranged in a molded insulation shell, the circuit breaker poles are uniformly arranged at the two sides of the residual current trip device, adjacent circuit breaker poles at each side share a composite operating mechanism which is used for controlling the on and off of a movable contact and a static contact, each composite operating mechanism is provided with a handle, a trip connection rod pivotally arranged on a rotation plate and a trip rod. The residual current trip device comprises a residual current monitoring element, an electromagnetic relay, an auxiliary trip mechanism with an auxiliary handle, a rotation connection rod mechanically coupled with each composite operating mechanism and a test loop. A linkage element is in mutual mechanical connection and linkage with the auxiliary handle of the auxiliary trip mechanism of the residual current trip device and the handle of each of the composite operating mechanisms at two sides. By the low-voltage circuit breaker, a conductive loop of the circuit breaker poles is effectively reduced, rated current specification can be expanded into 40A, and the width is reduced by nearly one third compared with a spliced product.