The most important step of building a new airport is site selection. Before selecting the new airport site, Airport planners should study many factors and rank the various sites. In fact, airport site selection is a complex multi-objective optimization problem, which involves a variety of factors. Taking “the civil airport construction and management requirements” as a foundation, the paper has screened and expanded the influence factors of selecting the civil airport site and constructed site appraisal system, and put forward the DAGF model，which constructed Evaluation System by improved Delphi method, obtained weighted matrix by AHP, analyzed experts score by gray correlation and got evaluation findings by Fuzzy evaluating. Meanwhile the paper has compiled the procedure of the computation process with MATLAB. Finally the research results has been applied to the selecting site of the second Capital airport in practice and obtained the satisfactory result. Therefore the paper constructed the comprehensive evaluation model, which provides the effective method for selecting the civil airport site, and makes the site selection more scientific, more reasonable and simpler. It has the extremely important reference significance and the instructional function to select the optimal airport site.