The invention discloses an engine jet pipe with the throat diameter adjustable. The engine jet pipe comprises a jet pipe casing, a plug cone, a jet pipe convergence section, a jet pipe diffusion section, an energy storage mechanism and a mechanical locking device. The plug cone is fixed to the jet pipe convergence section, the jet pipe divergence section is movably arranged at the throat portion of the jet pipe, the energy storage mechanism and the mechanical locking device are arranged on the jet pipe casing, and the jet pipe convergence section can move in the axial direction of an engine under the effect of the energy storage mechanism in the working process of the engine, so that the relative position change of the plug cone and the throat portion of the jet pipe is achieved, and one-time change of the throat diameter of the jet pipe is finally achieved. The relative position change of the plug cone and the throat portion of the jet pipe is achieved through the energy storage mechanism in the engine jet pipe with the throat diameter adjustable, the diameter of the throat portion during work of the engine can be changed, and the high thrust ratio of the engine can be achieved.