Abstract: Glass/epoxy fiber composite laminates were prepared by the vacuum bag and the hot pressing process. The content, shape and distribution of voids were investigated. The several factors which affect the voids formation were studied, including the temperature condition, applied pressure, environmental moisture and the laminate lay-up type. The Kardos void formation model was used to analyze the experimental results. It indicates that the main factors affecting the voids formation change with different processing methods, and the distributions of voids in unidirectional composite laminates have significant coherence; the Kardos void formation model can be used to estimate the voids formation.