Abstract: The present invention provides an arc extinguishing structure for direct current circuit breaker, which comprises a first casing, a second casing, an arc extinguishing chamber, a gas generating hood, a movable contactor and a stationary contactor, with a plurality of arc extinguishing grid-plates installed at an upper part inside the arc extinguishing chamber and having lower slots which are open towards an accommodation space and have a size that gradually decreases along a direction from the second casing to the first casing, wherein the first casing has a first extension plate disposed against the first gas generating plate and a second extension plate disposed against the second gas generating plate, the first extension plate and the second extension plate are arranged to extend into the arc extinguishing chamber so as to form a spacing communicated with the accommodation space and disposed opposite to the arc extinguishing grid-plates.