Abstract: By analyzing typical operating regimes of Laval nozzle,a zero-dimensional pneumatic model was built to evaluate the influence of Laval nozzle on the performance of aero-engine.The Laval nozzle model was integrated into a whole aero-engine component-level model.Numerical simulations were performed to study transient performance of aero-engine when nozzle throat and outlet areas decreased during accelerating process from idle to middle state.Results show that low pressure rotor speed decreases during some specific regimes,along with the reduction of Laval nozzle area in accelerating process,which also exists in real aero-engine rig tests.Besides,after normal shock clinging to nozzle outlet section was pushed out,there was a mach number break from subsonic to supersonic in nozzle outlet section,however,both the outflow rate and thrust changed smoothly without any break at the accelerating curve.