In this paper, a method to accurately measure the supercooling of HgCdTe films grown by LPE has been proposed. Influences of supercooling on the thickness uniformity of HgCdTe films have been studied by combining with optical Microscope, Fourier transform infrared (FTIR), step profiler and White-light Interferometer (WLI). Results show that, thickness in the center of a 20 mm×25 mm film decreases when supercooling is less than 2℃, while it increases significantly with cross-hatch pattern when supercooling is more than 3℃. Thickness variation of a 20 mm×25 mm film could be less than 0.5 μm, and the surface roughness is comparable with CZT substrate when the supercooling is around 2.5℃.