Abstract: A stage by stage parallel compression system model is developed for predicting aerodynamic stability in the multi stage axial compressors with inlet steady state pressure and temperature distortions. A numerical technique based on bidiagonal schemes is used to solve the conservative equations. The predictions for a three stage axial compressor with inlet pressure distortion or combined pressure and temperature distortions are given. The relationships between inlet pressure distortion or combined pressure and temperature distortions and the surge margin losses are obtained. A quantitative criterion of predicting the first stage flow instability is presented.