Abstract: The number and karyotype of Fraxinus velutina chromosomes is researched,applying fingertip pressing flake method.The formula for karyotype:is reported in this paper.The number of Fraxinus velutina number of the somatic cell chromosome is 2n=22,which is K(2n)=22=20m+2sm and belongs to the type of "1A".The relative length of chromosome is 2n=22=4L+10M₂+8M₁.The purpose of this research is to provide foundations for the breeding and taxonomy.