Cadmium zinc telluride (Cd1-yZnyTe) single crystals are important material for infrared detectors fabricating process and radiation detectors. Cd1-yZnyTe crystal wafers are widely used as substrate to grow epitaxial layers of mercury cadmium telluride (Hg1-xCdxTe) that is an important process for infrared detectors with high resolution. Especially, Cd1-yZnyTe with small concentrations (y=0.03~0.04) is favored for this purpose since the lattice constant of Cd1-yZnyTe (y=0.03~0.04) is close to that of Hg0.8Cd0.2Te, which has a bandgap corresponding to 10 micron. These applications impose certain requirements on the Cd1-yZnyTe crystals. Impurity concentrations should be low, especially for Cu, which can readily diffuse into the epitaxial layer and alter its electrical properties. Dislocation etch pit density should be low, typically no more than 1×105 cm-2. Infrared transmission should be high, usually greater than 60%, from 2.5 to 20 μm. Precipitates, visible as dark spots in infrared transmission microscopy, should be no larger than 10μm in diameter, and their density no higher than 0.5×105~1×105 cm-2. This paper reports results on how these requirements can be met by our research and development works in Kunming institute of physics mainly through controlling the cadmium atmosphere pressure in the quartz ampoule.