At present, for the research of aero engine performance, it is necessary to calculate the overall thermal performance of the aero engine at the beginning of the research. For the mathematical model of the isentropic expansion (compression) process, most researchers use the ideal state value to calculate in the mathematical model, so that the calculated results have a certain error compared with the actual value. Therefore, the new isentropic expansion (compression) process mathematical model based on the Φ function is applied in this paper to the technical aero engine overall thermal performance calculation. After calculation and analysis, it is concluded that the calculation accuracy of the mathematical model provided in this paper is higher than that of the literature program for the overall thermodynamic performance parameters of the aero engine, whether it is the thrust of the aero engine, the unit fuel efficiency, or the thermal efficiency of the aero engine. It shows that it is feasible to revise and improve the mathematical model of isentropic compression and isentropic expansion process in this paper, more accurate calculation results can be obtained by using the new model in the performance analysis program, and more accurate numerical analysis can be carried out.