Abstract: Loaded by weights, glass fiber reinforced unsaturated polyester (GFRP) composites were immersed in chloride ion environment at regular intervals, the moisture absorption rate of GFRP was tested to study the moisture absorption law under different stress levels.The results show that the moisture absorption rate of GFRP increases quickly with time in the initial immersion stage, then the moisture absorption rate becomes slow.Moreover, the increasing of the immersion time beyond 180 d causes a gradual decrease of the moisture absorption rate.With the increase of the load, the moisture absorption rate of GFRP decreases.And the change law of moisture absorption rate with varying time is the same for GFRP specimens under different load levels.The moisture absorption behavior of GFRP immersed in chloride ion environment has been demonstrated to show non-Fickian feature.Based on Langmuir model and taking moisture absorption feature of materials mass loss due to materials hydrolysis into accounts, a moisture absorption model was proposed to describe the increase and down trend of mositure absorption curve of composites, which can predict the moisture absorption amounts of GFRP well.