Probing the liquid film at two wavelengths with different absorption cross-sections allows eliminating the effect of additional broadband signal losses, e.g., minor beam steering. However, severe beam steering effects due to the shrinking of the liquid film at the end of the evaporation process can not be avoided. The effect is studied by measuring the film thickness on quartz plate during film evaporation process with two-color tunable diode laser absorption spectroscopy (TDLAS) method, and shadowgraphy images are simultaneously taken to track the change of film shape. Severe beam-steering effects are reduced in the developed two-line TDLAS film-measurement sensor by using an integrating sphere in front of the detector. The sensor is then applied to obtain the film thickness variation in the flow channel during the film build-up by impinging of water droplets and the evaporation of liquid film.