Abstract: The glass fiber/ epoxy resin 648 variable thickness laminates were prepared with the hot press and the
autoclave methods. The mechanism of defect formation in the two processings was investigated , and the effect s of the lay-up type and ply-drop gradient on the extent and dist ribution of defect s were studied. The result s show that fiber asymmet ric dist ribution , rich resin and delamination are the major types of defect s. Two dimensional resin flow result s in fiber uneven dist ribution , which is influenced by the fiber discontinuous area , permeability of the fiber bed and the uniformity of applied pressure. Rich resin result s f rom the fiber discontinuous area. Delamination has close  relations with fiber dist ribution and anisot ropy in thermal expansion. The result s are valuable for eliminating the defect s and cont rolling the processing quality in variable thickness laminate st ructures.