During the liquid nitrogen shock process of the HgCdTe focal plane arrays detector,the thermal mismatch between the different layers of the HgCdTe focal plane arrays detector generates,because of the difference of the linear expansion coefficient in the HgCdTe focal plane detector which is composed by the layered materials.Once the generated thermal stress exceeds the fracture strength of HgCdTe chip,the fracture of the HgCdTe chip appears and limits the structural reliability of HgCdTe focal plane detector.In order to solve the thermal mismatch problem in the HgCdTe focal plane detector,with the help of MATLAB,the calculation method of thermal stress suitable to the linear elastic multilayer system is adopted,the thermal stress distribution in the HgCdTe chip along its normal direction with different thicknesses of the silicon ROIC is obtained.The calculated results show that the thermal stress generated in the HgCdTe chip decreases linearly with the thickness of silicon ROIC decreased from 340μmto 25μm.This changing tendency indicates that thinning silicon ROIC is an effective approach to solving the thermal mismatch problem in the HgCdTe infrared focal plane detector.