A simplified method for estimation of crack opening displacement δ in complex conditions is proposed in this paper. The expression for COD evaluation is a modification of the solution for the strip yield model, by Dugdale and Bilby et al., namely, δ= 8σ _YC /π E 1n {sec ( πσ /2σ _Y )} where, σ, c , σ _Y and E are equivalent applied stress, equivalent crack length, epuivalent yield stress and equivalent Young's modulus, respectively. These values are affected by the crack profile, stress state etc., and are determined, basically, as follows, σ is determined so as to assume the same value as σ _Y when the cracked section attains general yielding conditions. c is determined by ( K /σ)²/π in oder to satisfy the relation δ= K ²/ ( Eσ_Y ) under small scale yielding conditions. σ_Y and E are determined by considering the effects of the plastic constraint, deformation mode etc. The COD values of the cracks for which K values are known can be evaluated easily through the proposed method. It is verified that these COD values are, in general, larger and good approximations of the exact solutions by the strip yield model. The brittle fracture initiation stresses are estimated through COD concept using the proposed method and are compared with the experimental results. The relationships between COD and the overall strain in residual stress field and under bending stress are discussed using the proposed method.