Abstract: Experimental investigation of hypersonic laminar separation flow over a 3D wedge is carried out in the hypersonic wind tunnel by utilizing oil flow visualization technique. Two test models of rectangular/ triangular flat plate are used. The 3D wedges which have different compression angles are mounted on the afterbody of models. The experimental result shows that the forebody shape has a great influence on the structures of hypersonic laminar separation induced by the 3D wedge. For the triangular plate model, the flow in the upstream of the wedge has obvious crossflow effect, and the separation structure is completely different from that of the rectangular plate model. At different attack angles, the shapes of the separation lines are also very different. The result shows very significant 3D effect of the local laminar separation which is induced by the triangular forebody and the 3D wedge.