A 3-D elastic-plastic finite element analysis of fatigue crack closure for semi-circular crack is performed. The stabilization behaviour of crack opening level, the effect of mesh size, the effect of initial crack length, the opening process of crack surface and the shortcoming and sensitivity of experimental measurement methods are investigated. The crack opening load tends to increase with the decrease of mesh size. Irrespective of an initial crack length, all the first nodes behind the crack tip along the front of surface crack are the last to open. The plane strain-opening load at the deepest point measured by extensometer at the midpoint of crack mouth may be estimated to be higher than the actual. The crack opening load experimentally measured by strain gauge boned in the vicinity of the surface intersection point can successfully represent the plane stress crack opening of the free surface. (c) 2006 Elsevier Ltd. All rights reserved.