Using ray-tracing method,the performance of the ellipse lens and the coaxial double half-ellipse lens(CDHEL) used to collimate laser diode beams are discussed.The numerical results indicate that the collimating performances of two lens changed little as the increasing of the refractive index and this made it possible to choose the material of the lens in more field.Theoretically,the radiation angle of laser diode beams in the quick axis can be compressed under 0.1 mrad.