Abstract: The infrared frequency doubles parameters and element processes of CdSe crystals were studied. According to the infrared nonlinear optical theory and refractive index dispersion relation, the tuning curve of angular vs. Fundamental wavelength(5.5-10.0 μm) of the CdSe crystal at 100 ℃ was obtained, and from theory calculation, the azimuth angle of CdSe crystal could be discretionary chosen because it didn't influence the type Ⅱ phase matching effective nonlinearity d_(eff), which equal to d_(15) sinθ. However, calculation results of the effective nonlinearity on the type Ⅰ phase matching condition indicated that effective nonlinearity equal to zero, so CdSe crystal could not realize type Ⅰ frequency doubles. Further, for the CdSe crystal (grown by VUVG method) without any direction characters, based on CdSe crystal structure properties,a fast and new method to determine the optical axis by cleavage and XRD analysis was developed. The crystal was cut directionally, grinded and polished, and a type Ⅱ phase matching element with a size of 9.5 mm×9.5 mm×18 mm for 9.6 μm fundamental frequency was obtained preliminarily.