The invention relates to an ultra-low-NOx gas burner. The ultra-low-NOx gas burner comprises a central drum, a swirler, a gas gun group, a throat opening, a front panel and a shell; the swirler is arranged at a connector of the central drum, the throat opening and the shell are coaxially arranged on the periphery of the central drum, the gas gun group is composed of multiple inter gas guns, multiple middle gas guns and multiple outer gas guns, and the front panel is provided with opposite penetrating gas flow holes and outer gas gun nozzle containing holes; a central drum cavity is a center combustion-supporting air passage, an annular cavity between the central drum and the throat opening is a direct-current combustion-supporting air passage, and an annular cavity between the periphery of the throat opening and the shell is a cooling air passage; the inner gas guns and the middle gas guns are arranged in the direct-current combustion-supporting air passage, and the outer gas guns are arranged in the cooling air passage. In the working process, due to the fact that gas sprayed from the middle gas guns is transition gas, segmented configuration and staged combustion are achieved, sufficient combustion of the gas in the dispersed state can be achieved, the content of oxygen in a furnace hearth is effectively diluted, the emission amount of NOx is decreased to below 10 ppm, and CO is not generated.