Abstract: Damage is the most important factor that influences the load-carrying capacity of oil derricks.To correctly diagnose the damage,a novel identification approach to oil derricks is proposed based on two indices,stress and equivalent damage coefficient.Firstly,equivalent damage coefficient is taken as the synthetical index to identify the existence and degree of damage,based on which,the damaged stiffness matrix is established.Secondly,the functional relationship between stress and equivalent damage coefficients is determined,and the sensitivity expression of stress residual matrix to equivalent damage coefficients is built.After that,the objective function based on stress is constructed,the direct derivation and optimization method are applied to identify the equivalent damage coefficients.Finally,the method is demonstrated with some oil derrick.Resultsshow that single,two-damage and symmetry damage can be identified accurately.Compared with other static identification methods,it is more efficient and needs less working capacity.