Abstract: Some moisture absorption tests were carried on one-way fiber-up T300/648 composite in four kinds of environment(temperature of 71 ℃ and relative humidity of 70%,temperature of 71 ℃ and relative humidity of 85%,temperature of 85 ℃ and relative humidity of 70%,temperature of 85 ℃ and relative humidity of 85%).The moisture time was 0-9 000 h,and the moisture absorption characteristics,glass-transition temperature,storage modulus,chemical structure and the interface morphology between resin and fiber were studied.The results show that the moisture absorption curves exhibited linear growth and then became flat.The moisture absorption capacity was higher in the environment of higher temperature and relative humidity.With the increase of aging time,the interface between resin and fiber weaken,but the chemical structure of the composite had little changes,and the glass-transition temperature and storage modulus decreased gradually.Moisture absorption capacity is the main factor influencing the glass-transition temperature,and the interface property is the main factor influencing the mechanical properties.