The airport is an important infrastructure for the development of civil aviation industry, and whether the airport site selection is reasonable or not determines the operation of civil aviation and even the whole transport network. With the development of civil aviation industry, airports and routes increase rapidly, which makes airspace become one of the main limiting factors of airport site selection. First, this paper collects the geographic information of complex airspace area and uses Supermap software to build the geographic spatial database; then, according to the civil aviation airspace methods, analyzes the airspace structure of complex airspace area, vectors the airspace structure based on the geographic spatial database, and determines the airport site selecting area, which is not restricted by airspace through overlay analysis and buffer analysis; and finally, uses service area analysis to obtain the radiation range of existing airports and determines the optional area of the airport under the combination with the analysis of airspace structure. By analyzing living examples in detail, this paper puts forward a feasible solution for determining the optional area of the airport, which can provide a scientific basis for airport site selection.