The basic parameter for evaluating the efficiency of airport operations is capacity. Investment planning in the aviation industry is a complex process, requiring consideration of many factors and a combination of different aspects. The aim of the study is to present the possibility of using discrete event simulation as a tool for determining the capacity of runways at airports. The main research problem of the article is: How to build a simulation model for determining the capacity of an airport runway using FlexSim software? An attempt was made to build simulation model, the purpose of which is to carry out simulation analyzes of airport capacity, and in particular of the runway. Simulation analyzes were performed using the FlexSim 3D Simulation software. The article discusses in detail the operating principle of the model and presents the results of numerical tests carried out to calculate the capacity of runways and taxiways at airports. The constructed simulation model of the airport capacity in the FlexSim environment enables to determine the airport’s runway capacity, constituting valuable information to support modernization decisions. The model may contribute to the efficient adjustment of the runway capacity. It should be noted that the creation of an effective system dedicated to a given airport will improve the air traffic control carried out by the system based on calculated maximum hourly runway capacity.