Dugdale model is a very useful modelling method in order to investigate crack opening displacements even though the cracked body does not satisfy the small scale yielding condition. The fictitious crack for Dugdale model, which corresponds to plastic region ahead of a crack, has a certain opening displacement although this part is continuum medium in an actual condition. Physical meaning of the crack opening displacement of a fictitious crack in Dugdale model is investigated by comparing with elastic-plastic finite element analyses. Center cracked tensile specimen with various crack lengths is turned into an object of the analysis. Crack opening profiles including a fictitious crack and deformations ahead of a crack tip are calculated by applying the Dugdale model. The corresponding finite element analyses are also performed. It is confirmed that the fictitious crack opening displacement in Dugdale model has close association with the integration value of plastic strain for the vertical direction to a crack line under elastic stress with tensile yield stress level. That is, the fictitious crack corresponds to the plastic deformation condensed over a crack line and is interpreted as the source of plastic deformation ahead of a crack tip.