The work aims to study the effects of various process factors (hot-press temperature, hot-press pressure, and initial water content and basis weight) on the moisture transfer process of overloaded molded fiber material, and reveal the mechanism of moisture transfer in hot-press molding. The moisture change of molded fiber slab at different positions was measured in the method of interlayer design. The T test and F test methods were introduced to test the difference of water change curves at symmetrical position. During the hot-press process, the moisture content was symmetrically distributed in overloaded molded fiber materials and the moisture change could be divided into 2 stages: the rapid descending section (section Q) and the centralized vaporization section (section L). The moisture gradient mainly occurred in section L and its moisture transfer in turn met the steady state diffusion of Fick's first law and the unsteady state diffusion of Fick's second law. The diffusion rate gradually decreased from the outside to the inside. In sections Q and L, the increased hot-press temperature and pressure or the decreased basis weight could accelerate the descending rate of the moisture content of the core layer. The initial moisture content had no significant effect on the descending rate of moisture content. In hot-press process, the overloaded molded fiber material is dried from the outside to the inside. Reducing initial moisture content, improving hot-press temperature and pressure, or decreasing basis weight can shorten the drying time of overloaded molded fiber material.