[Objective] Leymus Hochst stands as a crucial genetic resource for the genetic improvement and breeding of cereal crops. However, as allopolyploids, their genome origin remains unclear. [Methods] Genomic Cot-1DNA library of Leymus secalinu was constructed, clones of which were sequenced and analyzed. A few of repetitive sequences were physically mapped in chromosomes of L. secalinus, L. racemousus, and Psathyrostachy juncea by Fluorescence in situ hybridization (FISH). [Results] (1)The repetitive sequences of the Cot-1DNA of L. secalinus could be classified into 4 types based on their expected genomic distribution patterns, tandem repeats (TaiI, Lt1-6, pTa535 and pSc250 family), dispersed repeats (retrotransposable LTR and transposable elements), tandem mixed dispersed repeats (LTR plus Afa-family and N8-family plus LZ-NBS-LRR), and uncharacterized repeats, and which represented 32.4%, 45.7%, 12.4% and 9.5% of the Cot-1DNA, respectively. (2) The hybridization sites number of tandem repeats TaiI, Lt1-6, pTa535 and pSc250 were highly varied from 7-20, 1-14, 17-26 and 0-24 respectively, across different species and accessions. (3) Ten LTR repeats hybridized the tested species chromosomes mainly by 3 patterns: First, hybridizations distributed in centromere, pericentromere, and intercalary regions in all chromosomes. Second, hybridizations were all over the chromosomes. Third, Hybridizations were as the same as the pattern 1 except a few chromosomes carrying telomeric hybridizations. Two LTR/copia sequences were detected only in L. secalinus, while the others were detected in all tested species and accessions but with polymorphisms in hybridization intensities or hybridization patterns in partial chromosomes. [Conclusion] The results suggested rather fast-evolving repetitive sequences in Leymus genome, and supported hypothesis that the dispersed elements must have spread across genomes, thus homogenizing the nuclear genomes of Leymus during the allopolyploidization process.