Abstract: The process procedure of composites has decisive effects on the mechanical strength of the end product, but the mechanics is rather complicated for the process. A set of cure pressures were applied to produce various void contents. Qualitative and quantitative characterization of porosity in terms of void distribution, shape, size and volume fraction was carried out by ultrasonic C-scan, microscopic analysis and acid digestion methods. Effects of porosity on the interlaminar shear strength, flexural strength and tensile strength for the laminates were discussed and the critical value of void content at which the strength began to decrease was also obtained. The results show that the effects of porosity on the strength are mainly attributed to the void content, void distribution, size and shape, and the void content has little connection with the generation method. The investigation of this paper correlates the process parameter, porosity and performance, and embodies the integrated characteristics of design, manufacture and performance of composites.