Abstract: Gust response analysis plays an important role in largeaircraft design. Most of existing aerodynamic models for gust responseanalysis are linear, not suitable for transonic nonlinear aeroelasticanalysis. In this paper, based on CFD technique and system identificationmethod, a CFD-based ROM (reduced order model) is firstly constructed instate space. Gust response analysis is then investigated by couplingstructural equations with CFD-based ROM. The case of a square-edged gustresponse for a typical wing is presented to obtain the responses ofgeneralized coordinates and root bending moment (RBM) and to validate thecorrectness and precision of the CFD-based ROM method, compared well withthe direct approach of a coupled CFD/CSD methodology