Abstract: The penetration of resin along thickness is one of the most crucial factors in liquid composite molding (LCM). The method of continuous loading was used to study the compressive behaviors of non-crimp fabric(NCF) and woven fabrics(WF) during the liquid molding of glass fiber reinforced resin matrix composite respectively and a mathematical model was established to describe this behavior. The through-thickness permeability K_z of the preform under gravity and different injection pressures was tested by a self-made through-thickness permeability testing device. The influence of the preform fiber volume fraction and injection pressure on K_z of the preform was studied. Based on the preform compressive behavior model and the dependence of K_z on injection pressure, the Kozeny-Carman formula was modified and a through-thickness permeability prediction model was presented. The results show that the through-thickness permeability decreases with the increase of the fiber volume fraction of the perform V_f, which agrees with the Kozeny-Carman equation. As the fiber volume fraction varies in the region from 0.42 to 0.58, injection pressure has significant influence on the permeability, and the accuracy of the prediction model presented here is validated experimentally. However, when the fiber volume fraction is higher than 0.58, the injection pressure has little effect on K_z and K_z tends to be constant as V_f increases.