In this paper, low temperature oxygen plasma treatment method was adopted to process the carbon fiber surface. Flexural Strength test method was utilized to represent f composite material flexural strength. This paper observed flexural failure morphology of composite material by aid of SEM, then it compared the mechanical property, hygroscopicitiy and flexural strength retention rate of composite material before and after the plasma treatment. Results showed that the optimum treatment conditions of carbon fiber were 300W treatment power and 15-minute treatment time. Under the condition, the highest flexural strength value be increased by 19.55%.Saturated bibulous is low and bibulous rate is slow, flexural strength retention rate is 94.9%. And at the same time PES-C resin matrix can be strengthened, which will further improve the mechanical properties of composite materials.
