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