The invention relates to an arc extinguishing chamber of a circuit breaker. The arc extinguishing chamber is arranged at one side of a contact mechanism of the circuit breaker and comprises an installation bracket, a first arc extinguishing grid sheet group and a second grid sheet group, wherein first grid sheet group and the second grid sheet group are respectively installed on an upper part anda lower part of the installation bracket along a closing direction of the contact mechanism, the first grid sheet group comprises a plurality of longitudinal grid sheets which are arranged at intervals, and the second grid sheet group comprises a plurality of transverse grid sheets which are arranged at intervals; and the first longitudinal grid sheet, which is the farthest from the contact mechanism, in the first grid sheet group and the first transverse grid sheet, which is closest to the first grid sheet group, in the second grid sheet group are connected in a conduction manner. According to the arc extinguishing chamber of the circuit breaker provided by the invention, the transversely arranged grid sheet group and the longitudinally arranged grid sheet group are set, and the longitudinal grid sheet, which is the farthest from a moving contact, in the grid sheet group arranged opposite to the moving contact and the transverse grid sheet, which is the farthest from a static contact,in the grid sheet group arranged opposite to the static contact are connected in a conduction manner, so that the direction of the arc is reasonably guided, the arc is lengthened to the maximum extent, and an effect of extinguishing the arc quickly and thoroughly is achieved.