Study on screening method of CdZnTe substrates for improving the quality of LW HgCdTe films grown by liquid phase epitaxy (LPE) is mainly presented. All of the CdZnTe substrate′s parameters such as Zn composition, infrared transmittance, deposition & precipitation, etch pit density (EPD), X-ray topography and XRD FWHM are tested. And X-ray topography and XRD FWHM of HgCdTe films grown by LPE are evaluated. We find that the X-ray topography and Zn composition are important parameters which affect HgCdTe film′s quality at present. The result shows that CdZnTe substrate involving appropriate Zn composition between 4.2% and 4.8%, and X-ray topography with good uniformity and high diffraction intensity is perfect for LW HgCdTe films grown by LPE.