High quality CdTe/Si composite substrate is grown by molecular beam epitaxy.We develop Hg1-xCdxTe/CdTe/Si which is an important infrared material and used for making infrared detector by MBE and LPE respectively.The infrared transmission spectrum of Hg1-xCdxTe/CdTe/Si by FTIR is analyzed and then the film thickness is calculated.The SEM measurement result is used for correcting.Finally,we establish a non-destructive,non-polluted,fast and convenient measurement method for multilayer film thickness.