In the manufacturing process of polymer materials, the materials often contain excessive ethanol solvents, which seriously affect the mechanical and combustion properties of the products. As a key step to remove residual solvent, the water immersion process faces challenges such as unclear kinetic mechanisms and an undefined quantitative relationship between process parameters and product quality. Based on the volume averaging theory and porous media model assumptions, considering the coupling among gas–liquid–solid three phases, this work proposes a dynamic simulation method for continuous water immersion, analyzes the evolution of solvent content under various operating conditions, reveals the kinetic mechanisms of the immersion process, and provides a theoretical basis and simulation tools for quality assessment and parameter optimization.