A new collimator is invented which is consisted of the graded-refractive-index(GRIN)-rod microarrays and diaphragm microarrays. The optical principle and the effects of material and structural parameters on collimating properties are studied theoretically. The results of calculation and preliminary experiments show that the quasi-collimating light with the low diffuse angle and small chromatism can be obtained when the parameters are chosen appreciatively. The collimator can meet the needs of collimating backlight of LCD.