The issue of mathematical modeling of aerodynamic characteristics of arbitrary ventilation systems is considered. The modeling methodology is based on their object decomposition. In accordance with the accepted approach, according to the design and technological features, typical design elements are distinguished in the system, which include: sources of pressure or superchargers; sections of air ducts; shut-off and regulating devices technological devices that discharge or select the working medium from the system. Based on the analysis of the spatial and technological structure of ventilation systems, structural nodes and closed contours are considered. The mathematical models of aerodynamic characteristics have been adopted for typical design elements, structural nodes and closed contours, which makes it possible to form the generalized mathematical model for studying the stationary regime of arbitrary ventilation system. The mathematical models are based on the equations of energy and continuity. Recommendations are formulated on setting the initial data for mathematical modeling, as well as setting boundary conditions. The methodology of conducting numerical procedure for mathematical modeling of aerodynamic characteristics of ventilation systems based on object decomposition is considered. The proposed approach has been tested in practical calculations of ventilation systems of industrial enterprises. The calculated values of the parameters of the gas-air flows are consistent with the results of experimental measurements.