Abstract: Double refraction and double reflection at the interface of two uniaxial crystals with arbitrary orientation of optical axis are analysed by the use of Snell's graphic method. Considering refractive index surface of uniaxial crystal and equal phases for incident light，reflected light and refracted light at the interface，directions of two reflected waves and two refracted waves can be plotted on the chart. According to the optic anisotropy of crystal，directions of light rays and polarizations corresponding to every light wave are analyzed. Based on geometrical relations of all vectors，expressions of the positions of reflected waves，reflected rays，refracted waves and refracted rays are given. The Snell's graphic method is simple and visual. The formulae are universality.

Key words: crystal optics, double refraction, double reflection, refractive index, phase