Corrections of CTOD for constraint loss in structural components in large-scale yielding conditions are made on the basis of the Weibull stress fracture criterion. A CTOD ratio beta = delta3p/delta(WP) is defined (beta < 1), where delta(WP) is the CTOD of a wide plate component and delta(3p) is an equivalent CTOD of the standard fracture toughness specimen at which the toughness specimen gives the identical Weibull stress with the wide plate. The CTOD ratio beta is decreased to a large extent after full yielding, which is more significant for a high yield-to-tensile ratio and a deep surface crack in the component. The Weibull modulus m exerts a marginal influence on beta. The use of the CTOD ratio beta in the structural performance evaluation eliminates an excessive conservatism, that is frequently experienced in the conventional fracture mechanics methods.