A numerical simulation of internal performance for an axisymmetric vectoring exhaust nozzle was conducted by applying a 3-Dviscous flow program.The effects of model scale and flow temperature on the results of simulation were investigated and the results of the simulation were compared to those of scale model experiments.The internal performance of a real engine in design condition was obtained and the effects of different geometrical angles and nozzle pressure ratios(NPR) on it were discussed.The investigation shows that: model scale and flow temperature have little effect on the internal performance;the results of scale model experiments can truly represent the internal performance of a real engine in design condition;the axisymmetric vectoring exhaust nozzle has excellent internal performance in design condition;and both geometrical angle and NPRaffect the internal performance.