The invention provides an arc extinguishing structure of a direct current circuit breaker. An arc extinguishing chamber is mounted on a second shell and provided with a side opening opposite to a first shell, a gas producing hood is mounted below the inside of the arc extinguishing chamber and comprises two opposite gas producing plates and a blocking plate, the blocking plate is opposite to the side opening and close to the second shell, a dynamic contact and a static contact are mounted in a mounting space, and the breaking positions of the dynamic contact and the static contact are located in a containing space and closed to the blocking plate; when the dynamic contact and the static contact break and generate electric arcs, the gas producing plates and the blocking plate are triggered by the electric arcs, and a large quantity of gas is generated to push the electric arcs to move in the direction away from the blocking plate; the sides, facing the containing space, of arc extinguishing grid pieces mounted on the upper portion in the arc extinguishing chamber are provided with lower openings, the size of the lower openings is gradually decreased in the direction from the second shell to the first shell, and the electric arcs are continuously blocked by the arc extinguishing grid pieces with the lower openings smaller in the moving process, cannot rush out of the side opening of the arc extinguishing chamber and can only enter the space among the arc extinguishing grid pieces to be extinguished as soon as possible.