The invention discloses a condensing gas water heater comprising a main heat exchanger, a condenser and an atomizer. The main heat exchanger is provided with a first flue gas passage and a second water passage. The condenser is provided with a second flue gas passage and a second water passage. A second flue gas inlet of the second flue gas passage is communicated with a first flue gas outlet of the first flue gas passage. A second water outlet of the second water passage is communicated with a first water inlet of the first water passage. An atomizing outlet of the atomizer is connected between the first flue gas outlet of the first flue gas passage and the second flue gas inlet of the second flue gas passage. The condensing gas water heater according to the embodiment has the advantages that the atomizer helps increase steam content of high-temperature flue gas so as to increase potential heat released by the flue gas, and heat exchanging efficiency of the heater is improved.