The work aims to build theoretical modeling to analyze the forming mechanism of coating thickness, so as to accurately control the coating thickness. Based on mechanism analysis and appropriate assumptions, the mathematical model of the flow process of Newtonian fluid at the micro gap between storage roller and metering roller of five-roll coater was established. The relational equation of coating thickness and its influencing factors was derived, and the key factorsthat affected the liquid film thickness were analyzed accordingly. A numerical simulation of flow process was carried out with CFD software. The rationality of boundary conditions and results derived from theoretical modeling and theories was analyzed through simulation flow field. The results showed that the theoretical modeling was consistent with the simulation flow field. The theoretical results and the simulation results were of higher goodness of fit. Therefore, such theoretical modeling was probably very reasonable. The theoretical results showed that the factors affecting coating thickness were coating liquid viscosity and surface tension, metering roll speed, roller diameter and gap between rollers. These factors and the coating thickness had quite complicated relation equitation. The research results help to find the most appropriate process parameters rapidly to obtain ideal film thickness in engineering practices.