Abstract: Infrared thickness measurement is one of the main methods of online film thickness measurement, but traditional infrared thickness measurement method still has such defects that it is sensitive to the stability of light source and it is not applicable to high-speed film production line. In order to solve these problems, a dual-light path reference measurement method was used and a dual-light path infrared thickness measurement system was presented. In the system, the light source is divided into measurement light path and reference light path, using a single CCD connecting both the measurement light and the reference light as light intensity sensor. The imaging principle was described and the applicability of the system for Lambert law was discussed. Finally, calibration experiments for polyethylene and polytetrafluoroethylene film were conducted to demonstrate the accuracy. The experimental results show that the method has high precision and good robustness, and can effectively avoid the impact of the unstable of light source.