Based on the adjoint data assimilation model and the positive model of unstructured triangular meshes and finite volume method,a formula for inversing wind drag coefficient is developed.The wind drag coefficient is automatically calculated by the numerical iteration process of intra-region observations.A series of adjoint data assimilation numerical experiments of generalized estuary are carried out successfully,indicating that:1)the method is correct and effective;2) the enough observed data can improve the inversion precision;3)the wind velocities of 10 m/s or 15 m/s have little influence on the inversion result of wind drag coefficient.