关键词: 对称性, 反射, 折射, 直线传播

Abstract: The space and time symmetrical properties of optical wave and the medium have been analyzed. According to the symmetry principle the time translation symmetry and some of the space translation symmetry have to be preserved during light propagation，reflection and refraction processes，and the three geometrical optic laws of rectlinear propagation law，reflection law and refraction Snell’s law are derived. The symmetrical analysis here explicit that the symmetry principle is of fundamental importance and is the basement governing the optical processes.

Key words: symmetry, reflection, refraction, linear propagation