Aerodynamic principles and the assumption of axial inextensibility of a two-dimensional flexible plate were used to derive a nonlinear theoretical model of flag flutter, investigate and analyze the coupled motion characteristics of flexible flag and airflow in nature and wind energy collection fields, and examine the effects of length, mass ratio, and wind speed on its motion characteristics. The flag oscillation process in the wind was numerically simulated using the bidirectional fluid-structure coupling method and the overlapping mesh methodology, from which the features of the surrounding flow field and the motion behavior of the flag inside it were determined. The findings indicate that while swing displacement increases and subsequently declines with wind speed, the crucial flutter wind speed lowers as flag length increases. The chirp frequency decreases as the mass ratio increases, and the Strahl number is less affected. With the predefined dimensions of the flag, at low wind speeds, both the displacement and frequency of the swing are low. However, when the wind speed exceeds the critical vibration threshold, a significant vibration phenomenon occurs. Changes in surrounding pressure and velocity are caused by the flag-encircling vortex as it progresses through phases of formation, shedding, and disappearing. Numerical simulation techniques based on the overlapping mesh methodology successfully address the deformation problem of flexible flags. Theoretical and numerical simulations can be verified and analyzed with this method.