The invention discloses a novel steam injection boiler tail flue system and belongs to the technical field of steam injection boilers. A tail flue comprises a condensation heat exchanger, a water discharging pipe, a tail curve and a chimney. The tail curve is in an L shape, and a flue gas outlet is arranged upwards and communicates with the chimney. The condensation heat exchanger is arranged at aflue gas inlet of the tail curve, and a condensate water groove is formed in the position, below the condensation heat exchanger, of the tail curve. The water discharging pipe is arranged below the condensate water groove and communicates with the condensate water groove. By means of the novel steam injection boiler tail flue system, the transverse space of a boiler can be sufficiently utilized,the flue where a convection heating face is located is arranged transversely, the overall height of the boiler is effectively reduced, and the transport difficulty is lowered; and the condensate watergroove is machined in the bottom of the transverse flue where the convection heating face is located, the problem about condensate water discharging and the problem of low-temperature corrosion can be effectively solved, the heat efficiency of the boiler is improved, the service life of the boiler is prolonged, and a good application prospect is achieved.