The invention relates to the field of combustion equipment and discloses a gas burner with low heating value. According to the gas burner, an internal combustion air pipeline and an external combustion air pipeline are adopted to provide combustion air separately; the combustion air provided by the internal combustion air pipeline is mixed with flue gas in advance to provide oxygen needed at the ignition earlier stage of fuel gas; the external combustion air pipeline provides flue gas to burn out the demanded oxygen so as to realize graded supplementation of the combustion air. The downstreamend face of the internal combustion air pipeline is arranged on the upstream of the downstream end face of the external combustion air pipeline to enable the combustion air provided by the external combustion air pipeline to be mixed with fuel gas in a delayed manner, so that on one hand, the ignition heat demanded by the earlier stage ignition of the flue gas is reduced to facilitate stable ignition of the flue gas with low heating value, and on the other hand, at the combustion earlier stage, the flue gas is at the oxygen-deficient environment, the reducing atmosphere is formed and kept conveniently, a high temperature area is not generated, and the formation amount of NOx is reduced.