With plant geography methods,combined with field investigation and historical documents,original forest area in north Greater Hinggan mountains in lnner Mongolia,floristic composition and geographical composition were analyzed.The results showed that:1) the Greater Hinggan mountains in lnner Mongolia have the original vascular plants of 92 families,373 genera and 1062 species(including varieties and forms),angiosperms accounted for 84.78%,93.57%,95.76%,of vascudle bundle plants in plots,the absolute advantage in number;in the division level,single section and small and medium-sized obvious advantages,accounting for 82.5% of the total families;on the relation between levels,including more than 20 kinds of larger families,the genera and species respectively accounted for 62.61% of the total 68.69%,these large families in floristic composition in this area has obvious dominance.2)The species/families indexes can well reflect the floristic intensity of differentiation,the kind of family was 12.78.3)Floristic geographical composition diversity with obvious temperate nature is given priority.The number of genera accounts for 89.12% of the total number of genera,genera number of tropical distribution accounts for 5.78% of the total number of genera of tropical distribution,which shows some linkage with tropical flora in this area,genera of the world distribution accounted for 16.71% of the total number of genera.This shows the universality of plants in this area.4) There are a total of 6 kinds of national key protectected wild plants in this area.In the Grester Hinggan Mountains there are three endemic species.