The local buckling analysis of thin walled member is generally conducted by modeling each plate component as an isolated plate with elastically restrained boundaries. When this analytical model is used for the orthotropic flexural members, it is necessary to obtain the degree of elastic restraint provided by adjacent plate. In this study, the equation to find the coefficient of elastic restraint by adjacent plate components of an orthotropic box-shape flexural member was derived by employing the energy approach, and the factors affecting the elastic restraint were briefly discussed. Using the suggested equation, the coefficient of elastic restraint was calculated, and the local buckling analysis was conducted according to the stepwise analytical procedure published by the authors. The theoretical predictions were in good agreement with results obtained by the closed-form solution. The local buckling strength of an orthotropic box-shape flexural member can be easily obtained through stepwise analytical procedure with the proposed equation that accounts for the effect of elastic restraint imposed by adjacent plate components.