Abstract: The 90° L-shape laminates under different conditions were prepared in the vacuum-bag process with the convex tool for unidirectional glass fabric/epoxy resin, and the state of the fiber compaction and defects at different positions were investigated. The experiments were designed to study the effects of the processing conditions on the defects. The results indicate that the redundant resin, void, thickness variation and fiber buckling are the main defect types in the L-shape laminates. In addition, the time of applying pressure, laminate dimension, type of lay-up and edge conditions have significant effects on the fiber compaction and the forming of defects. The mechanisms of the defects forming were analyzed. The thickness variation and the redundant resin are caused by shear flow, the fiber buckling results from axial compression, and entrapped air is the main source of void under the experiment conditions. The results provide important guidances for defects control and processing parameters optimizing in the hot press process.