The utility model relates to an instantaneous tripping mechanism for a miniature circuit breaker. According to one aspect of the utility model, the instantaneous tripping mechanism comprises a tripping rod, a double metal plate, a first magnet and a second magnet, wherein the tripping rod can rotate by taking one side as a center and move to a tripping position; and the tripping rod can move to a release position where a switching mechanism of the miniature circuit breaker is released and a restriction position where the switching mechanism is restrained; the double metal plate is electrically connected to a circuit and bends toward the tripping rod side when abnormal current occurs in the circuit so as to enable the tripping rod to move to the release position; the first magnet is conductively connected to the circuit and installed at the position adjacent to the double metal plate, and magnetized when abnormal current occurs in the circuit so as to enable the double metal plate to bend; and the second magnet is combined with the tripping rod, and enables bending of the double metal plate to be accelerated when abnormal current occurs in the circuit. The instantaneous tripping mechanism of the miniature circuit breaker has the beneficial effect of ability of shortening the time of instantaneous tripping.