Abstract: The probe of contact measurement interferes with the liquid film flow so that the precision is difficult to be improved. The application of the traditional optical method is limited because of the light refraction. In order to solve this problem, a new method was put forward to measure the dynamic film thickness using planar laser-induced fluorescence technique in this paper. The principle and implementation of the technique were introduced in detail. The timing characteristics and vertical evolution of free film were studied based on the real-time measurement along the film flow. The results indicate that the probability density distribution of film thickness is different which can be used to diagnose the wave characteristics.