Abstract: In this paper a new method of aerothermodynamic calculation for gas turbines and air breathing jet engines is offered. The main contents of this method are. ( 1 ) Introducing a new thermodynamic parameter caked specific enthalpy difference, a series of charts are established for calculating isentropic process of combustion gases produced from fuel CH2, so that the calculations can be simplified with sufficient accuracy. ( 2 ) After analyzing combustion gases produced from fuel "CHn" and "CHnOmNp", correction methods for calculation their thermodynamic properties have been found. ( 3 ) In order to use computers in above calculations analytical formulae with an accuracy of about 0.150o are provided.