A cladistic analysis of the genera in the family Fagaceae is made in the present paper．As a monophyletic group，the family Fagaceae includes 6 genera，namely，Lithocarpus，Castanopsis，Castanea，Trigonobalanus，Fagus and Quercus．The Betulaceae and Nothofagaceae were selected for outgroup comparison after a careful consideration．Twenty five informative characters had been used in this study．Three principles：outgroup comparison，fossil evidence and generally accepted view points of morphological evolution，were used for polarization of the characters．

    A data matrix was constructed by 7 ingroups，2 outgroups and 25 characters．The data  matrix was analysed with the Maximal Same Step Method，Group Union Method and the  Synthetic Method．Three cladograms were constructed and a parsimonious cladogram  (Lenth=75)was used as the bases in discussing the intergeneric systematic relationships in  Fagaceae．

In the Fagaceae，the first differentiated group might be the extinct common ancester of the extant genera Lithocarpus，Castanopsis and Castanea．They are reasonably with the distinct characters：mixed inflorescence or androgynous and the female flowers with staminodes．Among the three genera，Lithocarpus was differentiated earlier than the others and it remains more primitive (entire leaves；smaller diameter of vesseles；scanty tylose；cupule scaly appendages；mixed inflorescence and the female flowers with well developed stamens in some species)，Castanopsis is closely related to，but more primitive than Castanea．

As in a clade group，the genus Trigonobalanus orginated apparently later than the ancester of Lithocar- pus，Castanopsis and Castanea．Fossil evidence suggests that this genus originated as early as in the Paleocene to Eocene．And some characters，for example，leaf with   glandular peltate trichomes，chromosome number 2n=44，are only appeared in Trigonobalanus．Three species in this genus are disjunctly distributed in tropical Asia and South America，this genus is considered as both an isolated and primitive taxon in the Fagaceae，and it is also probably paraphyletic with the subfamily or tribe categories in this family.

      As shown in cladograms 1 and 2,the genus Fagus forms an isolated clade which consists of a relatively advanced taxon in the Fagaceae (with fiber tracheid and the reduction of the inner integument).

     In three cladograms,the clade of Quercus is the most advanced one,which is consistent with the current view-point about the systematic position of the genus Qucrcus and the concept of Qucrcus (s. l. ) in Fagaceae.

     The following conclusions may be reached by the author: (1) The six genera in the Fagaceae evolved in four parallel lines phylogenetically ,so they could be treated as four independent subfamilies,namely Castaneoideae ,Trigonobalanoideae,Fagoideae and Quercoideae ; (2) Parallel evolution is the main form in the phylogeny of the Fagaceae,some characters of the reproductive cycle, for example, fruit becoming ripe in the next year and the abortion of ovules etc. are the main factors which affect the gene flow among the genera in the Fagaceae; (3) In the Fagaceae, Lithocarpus is a primitive genus, and Trigonobalanus and Castanopsis both are also relatively primitive,but Castanea,Fagus and Quercus are relatively ad-