In order to study the problem of falling film flow characteristics on the vertical wall, the liquid film thickness measurement method based on planar laser-induced fluorescence method was studied. The corresponding relationship between image grayscale and thickness was obtained through a liquid film thickness calibration device. An overflow type falling film flow cycle experimental system was constructed and the falling film thickness on the vertical wall under different volume flow rates was measured. At the same time, numerical simulation of vertical wall falling film flow under different Reynolds numbers were conducted under corresponding experimental conditions. The relative deviation between the experimental measurement results and the numerical simulation results of the liquid film thickness is 5.5% at least and 11.4% at most. On this basis, the influence of Reynolds number on the thickness of falling film on the vertical wall was mainly studied. The results show that wall shear stress and gas-liquid interface shear stress are the main factors leading to liquid film fluctuations. As the Reynolds number increases, the surface fluctuation of the liquid film intensifies due to the difference between wall shear stress and gas-liquid interface shear stress caused by the increase in liquid flow velocity. In addition the amplitude of the liquid film fluctuation increases.