Abstract: Saur tarbagatai mountain range lies on the northwest of Jungar Basin,where the geographical position is special on the edge of the florae of Central Asia,Mid Asia and Siberia.Obviously,this flora has transitional characteristics.The resemblant relationships between this place and four other adjacent regions Tianshan mountains,Altay mountains,Kazakhstan and Inner Mongolia were analysed by using 12 formulae of similarity coefficients and discussed according to the method of calculating the cross set in the set theory.The result shows that the florae of the Saur tarbagatai mountains and Altay mountain had a closest resemblant relationship,and these florae maintained a close link with the flora of Tianshan mountains.There were obvious differences between the flora of Saur tarbagatai mountain range and that of Inner Mongolia.It proves that the flora of Saur tarbagatai mountain range is the passageway between the south flora and the north flora,and it has a little interflow with the flora of Inner mongolia.