The invention discloses a gas water heater. The gas water heater comprises a shell, a combustion device, a heat exchanger and a flue gas pipeline, wherein a containing cavity is defined in the shell; the combustion device is arranged in the containing cavity, and a combustion chamber is defined in the combustion device; the combustion device is provided with a gas inlet, an air inlet and a flue gas outlet, and the gas inlet, the air inlet and the flue gas outlet communicate with the combustion chamber; the heat exchanger is arranged in the combustion chamber; the flue gas pipeline is arranged in the containing cavity and provided with a gas inlet end and a gas outlet end; the gas inlet end communicates with the flue gas outlet to discharge flue gas in the combustion chamber; the gas outlet end communicates with the air inlet to supply flue gas in the flue gas pipeline into the combustion chamber. According to the gas water heater, generation of NOx can be inhibited, and emission of NOx can be reduced. Meanwhile, a small amount of CO which is incompletely combusted in flue gas can conduct a combustion reaction with the air so as to reduce emission of CO, improve the thermal efficiency and reduce gas consumption. Accordingly, the purposes of energy conservation and emission reduction are achieved.