The invention provides a pulse detonation engine tail nozzle. The pulse detonation tail nozzle comprises a convergent section, a divergent section and secondary flow introducing pipes. The secondary flow introducing pipes are communicated with the convergent section and the divergent section. The secondary flow introducing pipes are evenly distributed in the circumference direction of the tail nozzle. Each secondary flow introducing pipe is divided into a convergent section connection section, a divergent section connecting section and a curved section, wherein each convergent section connection section is parallel to the central axis of the tail nozzle, the axis direction of each divergent section connecting section is perpendicular to the a divergent section curved surface and the center line of the tail nozzle, the radius of each secondary flow introducing pipe is not larger than one tenth of the radius of the throat portion of the tail nozzle, and the total area of secondary flow injection holes formed in the tail nozzle divergent section accounts for 3%-8% of that of the throat portion of the tail nozzle. The pulse detonation engine tail nozzle does not depend on a huge secondary flow air supply system, self control of the effective divergence ratio of the pulse detonation engine tail nozzle within a period is achieved through adjustment of a divergence angle, and therefore an engine is still in the ideal working state in the detonative wave discharging stage, the filling stage and the blow out stage.