Abstract: Using Elymus excelsus Turcz. as the material and 45S rDNA and 5S rDNA as probes, through the distribution characterics in chromosome of 45S rDNA and 5S rDNA, of which the chromosomal karyotypes were analyzed by fluorescence in situ hybridization（FISH）. The results showed that hybridization signals were detected on the end of short arm of chromosome 2 and chromosome 20 and on the secondary constriction of short arm of chromosome 17 in 45S rDNA. Hybridization signals were detected on the short arm of chromosomes 2, 7 and 14 and on the secondary constriction of the short arm of chromosome 17 in 5S rDNA. The karyotype formula was 2n=6x=42=30 m+12 sm（4 sat）. The average length of chromosomes was 12.68 μm, the length of chromosomes ranged from 9.19 to 17.39 μm, and the total length of chromosomes was 266.29 μm. According to the principle of Stebbins karyotype classification, the karyotype of the Elymus excelsus Turcz. was 2A.