Abstract: Experiments and finite-element-method(FEM) analysis have been conducted to investigate the effect of a large size elliptical cutout on the stress/strain concentration and buckling, post-buckling behaviour of a square composite laminate under in-plane shear load. It is observed that the stress/strain concentration near the vicinity of cutout is considerable and the stability of the laminate declines remarkably due to the large cutout. The post-buckling loading capacity of laminate structure with a cutout is specific high. The failure modes of the test panel evaluated by experiments show that the high inter-laminar stress induced by the bending of laminate leads to the local damage of delamination companied by the fibre matrix shear-out. And with the structure’s horizontal deflection increasing, the fibre in the stress/strain concentration area is stretched to fracture resulting in the whole laminate collapsed instantaneously. The FEM analysis results agree well with the experimental results.