This work describes the development of a global model of a modified turbojet engine for dynamic behavior simulation. The Modelica language is used for the simulation of this model. A Modelica package was created for the basic components suitable for such models. The model is based on a general turbojet engine and a turbofan engine. The engine component models are established on the equations obtained from thermodynamic, aircraft propulsion and other public domain gas turbine literature. The aerothermodynamics of engine components (diffuser, compressor, combustor, turbine, nozzle and fan) are described and how they are modeled in Modelica. Due to having no specific engine model, a NASA TM 101433 Compressor Map and a NASA TM 83655 Turbine Map was chosen to model the compressor and turbine. When modeling engine components, especially for the compressor and turbine there was a very large amount of data that needed to be processed. The program Smooth C (for compressor) and Smooth T (for turbine) were used to enhance the efficiency and accuracy of data processing.