Modeling and simulation of gas turbines was a hot research direction at home and abroad. In this paper, micro-turbojet JetCAT-P80, a aviation gas turbine, was took as the research object, which the thermodynamic parameters of the various sections and the engine performance parameters of the design conditions were solved with the Matlab software. On this basis, GasTurb, a system-level modeling and simulation platform for gas turbine, was introduced. During a certain simplification of the premise, the simulation model on computer for Jet CAT-P80 aviation gas turbine was established, and the steady performance of the off-design conditions was studied, also the impact of external environment on gas turbine relevant performance parameters was detailed analyzed. The results show that the simulation results accurately reflect the steady state performance of gas turbine, and the error between the simulation result and the gas turbine actual operating parameters was within reasonable limits which verify the correctness and rationality of the model established in this paper.