Abstract: A mathematical model for real time simulation of twin spool turbojet engine has been established,which comprises a linearized compressor characteristics model,simplified turbine characteristics and the dimension reducing method of non linear equation set.Under the identical regime and inlet flow conditions,the performance of the twin spool turbojet engine was simulated respectively by real time model and non real time model.The results of the simulations were compared with test data.Favorable results of the comparison give the validation of the fundamental hypothesis of this study.This model makes a very good compromise between computation speed and accuracy,and has good convergence.