Taking the oil system of certain aero-engine as a study object,the paper analyzes in-depth the working principles of the oil system and the structure characteristics of its components.Formulas for calculating the oil pressure losses in the pipelines and the mathematical model of the components are established by using fluid dynamics,engineering thermo-dynamics and numerical calculation and experimental data.Finally,the steady pressure model of the oil system is established according to the data acquired in the aero-engine oil system in good conditions,and the results by using this model provide the reference for judging the performance attenuation and the fault of the oil system.The method of this paper can also be used for other aero-engines and its application value bears universality.