The composite substrates of lattice graded buffer layers of Si/ZnTe /CdTe for HgCdTe ep itaxy are studied to supp ressmismatch dislocations at Si/HgCdTe interface. The technical problems in CdTe growth on Si are solved, such as low temperature cleaning treatment of Si, controlling of polarity and twinning supp ression. The composite substrates of Si/CdTe (211)B with large area are obtained. The average FWHM value of 83 arcsec of 4 - 4. 4μm Si/CdTe (211) B films is achieved, similarwith the results on GaAs/CdTe for the same thickness.