The invention relates to the field of combustible gas downdraft coke ovens, in particular to a coke oven combustion chamber flue with an optimized structure. The flue comprises tubular bricks and a partition wall, and is characterized in that: the flue is realized by lengthening the travel of a combustible gas in the flue and forming a combustible gas passage in the flue along the travel, wherein the partition wall and the tubular bricks form a semi-enclosed structure along a horizontal direction; the partition wall is provided with a gas flow passage above the tubular bricks along a vertical direction; and the gas flow passage is provided with a groove-shaped gap with the width of between 10 and 35mm and the height of between 10 and 10,000mm. Compared with the prior art, the flue has the advantages that: because a gas outlet has a narrow groove structure, the diffusion speed of the gas is limited; the contact area of the gas and a combustion-supporting gas at the bottom of the flue is reduced, so the combustible gas is diffused from bottom to top along the groove-shaped gap, the combustion-supporting gas is excessively distributed in the flue and the flame is elongated, which is favorable for improving the uniformity of the temperature distribution in the flue; and meanwhile, because the partition wall becomes wider, the structural strength of a coke oven combustion chamber can also be improved.