One of the main methods to reduce the HgCdTe/Si dislocation density is to reduce CdTe/Si composite substrate′s dislocation density.How to improve the CdTe/Si composite substrate′s crystal quality is very critical for HgCdTe/Si FPAs.The general methods to reduce CdTe/Si composite substrate dislocation density are: growth of superlattice buffer layer,Si substrate misorientention and annealing etc.This paper presents the result of the influence on the quality of CdTe/Si composite substrate by Ex-situ annealing.The research indicates that after Ex-situ annealing，the EPD of composite substrate can reduce to 4.2×105 cm-2，and the FWHM can reduce to 60 arcsec.