In order to describe the unsteady aerodynamic characteristics of an aircraft in post-stall maneuvering, this article studies the unsteady aerodynamic modeling in the form of nonlinear differential equations. In view of its physical mechanism based on dynamic system modeling, the identification method using data from forced oscillation wind tunnel test is investigated. Based on data from small-amplitude experiments, the linear regression method is used to find the linear parameters such as the time constants, while genetic algorithm is used to identify the nonlinear correction terms based on data from large-amplitude experiments. Wind tunnel test with a model delta wing plus a center body are used to verify this method. The result shows that the model is able to predict the unsteady aerodynamic loads accurately in different movements, which bears proof on the practicality of the flight dynamic analysis.