The invention discloses a fume waste heat recovering device for a gas-fired boiler. The device comprises a combustion chamber, wherein a boiler body is fixedly connected to the top part of the combustion chamber; the upper part of one side of the boiler body communicates with the other side of an air preheater through a fourth pipeline; a water inlet of a heating pipe communicates with a water pipe through a water inlet pipe; one end of the water pipe communicates with the top part of a water tank; a second water draining pipe is arranged at the bottom part of the water tank and communicates with a first water draining pipe; and one end of the first water draining pipe communicates with a water outlet of a heating pipe. According to the device, the heating pipe coils the outer side of theboiler body, and heat produced by the boiler body can be used for heating water in the heating pipe; fume is charged into a spiral pipe, and the waste heat of the fume is utilized for heating the spiral pipe, thus the water in the water tank can be heated through the spiral pipe, and as a result, the waste heat recovering and use rate can be increased.