1 259 ground mosses specimens collected from Sygera Mountains （west slope） of Southeast Tibet were sorted and identified. The results show that there are 82 species of ground mosses in 47 genera belonging to 15 families in this area. The dominant families are Bryaceae， Dicranaceae， Pottiaceae， Polytrichaceae， Brachytheciaceae， Hypnaceae， and Mniaceae， and the number of species in these families accounts for 78.1％ of total species number of ground mosses in this area. The dominant genera are Pohlia Hedw.， Brachythecium Schimp.， Dicranodontium Bruch et Schimp.， and Plagiothecium Schimp.， and the number of species in these genera accounts for 30.5％ of total species number of ground mosses in this area. There are 10 dominant species accounting for 12.2％ of total species number of ground mosses in this area. It is suggested that the dominant families play a leading role in ground mosses of this area.