The present paper deals with the karyotype analysis of 10 species of Cupressus including C. arizonica, C. bakeri ssp. mathewsii, C. chengiana, C. duclouxiana, C. funebris, C. goveniana, C. lusitanica, C. macrocarpa, C. pygmaea and C. sargentii. Except for C. arizonica, C. chengiana and C. macrocarpa they are all reported for the first time.The karyotype formula of the 10 species is K(2n)=22=22m which belongs to Stebbins‘1A type. After making comparison among the karyotypes of 13 representive species in Cupressus, combined with data from geography, fossil, palaeogeography and palaeoclimate, the author thinks that C. sempervirens in Mediterranean region might be the most promitive one, the species in East Asia-China intermediate, those in North America advanced and C.lusitanica in Mexico and Guatemala the most advanced. The genus may have originated in the Mediterranean during the Jurassic or even earlier and then migrated from East Asia to North America via the Beringia in the Miocene or Pliocene. The regions, covering California, New Mexico, Mexico, Guatemala etc. are the present distribution center and the differentiation center of Cupressus.