Abstract: Hybrids F1 from distant hybridization of Trifolium ambiguum Bieb ev. Mengnong No. 1 and T. repens were highly sterile plants,which were just flowering instead of seeding over the past two years of the field planting. However, it started to fructification from the third year. In order to explore the seeding mechanism of F1 ,the technology of root tip chromosome tableting was used to identify the somatic chromosome of F1＇s seeds, meanwhile the condition of the tableting technology was explored and optimized. The results turned out that the somatic chromosome number in the seeds of F1 ranged from 40 to 48, and some cells of individuals emerged into chromosome doubling phenomenon and mixoploid. The chromosome number of somatic cells in F1 hybrids was 40,and 48 in T. ambiguum Bieb cv. Mengnong No.1. The somatic chromosome number of the 6-3% seeds was 44, which was initially identified as the resulting of backcross of F1 hybrids with T. ambiguum Bieb ev. Mengnong No.1 ,and its karyotype formula was 2n=30m＋ 14sin, which belonged to the type of 2A.