The invention discloses a turbofan engine and belongs to the technical field of design of an aero turbofan engine. The engine comprises a second afterburner (2) and a first afterburner (1), wherein the second afterburner (2) comprises an afterburner inner spraying pipe and a main force exerting cavity; the afterburner inner spraying pipe is fixedly connected with the back end of an inner cylinder;the main force exerting cavity is positioned in the afterburner inner spraying pipe; a through hole is formed in the afterburner inner spraying pipe; the first afterburner (1) comprises an afterburner outer spraying pipe and an auxiliary force exerting cavity; the afterburner outer spraying pipe is fixedly connected with the back end of an outer cylinder; the auxiliary force exerting cavity is positioned between the afterburner outer spraying pipe and the afterburner inner spraying pipe; the first afterburner (1) also comprises a baffle; the baffle is controlled by an adjusting mechanism to close or open the through hole in the afterburner inner spraying pipe; and the opening section of the tail end of the afterburner outer spraying pipe is adjustable. The length and the weight of the afterburner are reduced by adjusting the afterburning condition of the main force exerting cavity and the auxiliary force exerting cavity.