Exact prediction of unsteady aerodynamics is of great importance to the design and study of advanced combat aircraft. In response to the problem of complex calculating and lack of considerable factors in handling normal state-space model, a new flow separation model and a new state-space aerodynamics model are put forward in this paper. Compared with normal state-space model, complex calculation of differential equations is avoided and simultaneously a new influence factor -pitching angular velocity is introduced in the new state-space model which makes the physical meaning of the new state-space model proposed in the paper become clearer and more definite. At the same time, the static and dynamic proceedings are combined into one equation by the flow separation model proposed in the paper. At last, the large amplitude oscillation wind tunnel data are used for testing, the result suggests that the unsteady aerodynamic model proposed in this paper can describe the time-delay characteristics of the aerodynamic force and fit well with the wind tunnel test data.