Abstract:In the present paper,a new Flora Index i. e.Fij=(Lij/Cj)/(Li/C)is specially designed to resolve the comparative study on numerous regional floras,and its noral geographical and mathematical significance has been disscussed in detail.At last,the seed plant flora of Dujiangyan city and other 13 regional seed plant floras in China are shown to be examples by using floral index.