Abstract: The recent research shows that in right-hand anisotropic materials（such as common crystals） the negative refraction will also be taken under certain condition.It can be explained using the Huygens construction.In this paper the Huygens construction is used to elucidate that the double-positive,one positive-one negative,double-negative refraction may occur in the uniaxial crystals for a light beam including two wavelengths under the appropriate condition.The critical angle of incidence for occurrence neganve refraction is calculated for YVO4 crystal.This is beneficial for the students getting a right overall understanding while the left-handed materials and the negative refraction phenomenon are introduced in the teaching.

Key words: Huygens construction, uniaxial crystals, two wavelengths, negative refraction