Abstract: In aero engine modeling,Newton iteration method is often used to solve the non linear equations of engine model.But due to the strong non linearity of the equations,this algorithm often fails to converge at some points of the full envelope.In order to solve this problem,this article proposes a method to avoid iteration.Several variables and equations of volume dynamics in aero engine are introduced as complementary variables and equations,and as a result,the whole set of equations becomes closed form and can be solved without iteration.This method has been successfully applied to a turbofan engine and the simulation results show the feasibility and effectiveness of the proposed method.