Disclosed is a vehicle-mounted gas water heater, wherein the water flow pipe comprises a water inflow section, a first heating section, a second heating section and a water outflow section, wherein the water inflow section is shortened, wherein the water inflow section is shortened, a heating section is rapidly heated directly by the combustion heating device, and the second heating section is heated by winding on the heat exchanger, so that, formation of condensed water at the water inflow section is reduced due to reduction of surface area, condensed water formed on the surface of the first heating section is rapidly evaporated, and it is difficult for condensed water to form on the surfaces of the second heating section and the outflow section.