Amplified fragment length polymorphism(AFLP)technique was applied to assess the genetic variation among 4 fast growth families of Tegillarca granosa(J5♂×Z19♀,Z7♂×J26♀,S1♂×Z3♀,S6♂×Z22♀)so as to establish and select superior families. A total of 506 AFLP loci amplified with 9 pairs of primers were obtained from 124 individuals,and the polymorphic loci percentage reached 72.53%.The percentage of polymorphic loci of 4 families ranged from 51.14% to 60.75%.Nei’s genetic diversity index and Shannon’s genetic information index of 4 families indicated that the level of genetic diversity from high to low was J5♂×Z19♀＞S6♂×Z22♀＞S1♂×Z3♀＞Z7♂×J26♀.The gene differentiation coefficient G_ST value and AMOVA analysis indicated that the genetic variation mainly came from individuals within families.Genetic division coefficient F_ST (0.383 7)indicated that there was certain genetic differentiation that existed among the four families.Cluster analysis by NJ and UPGMA methods based on genetic distance revealed the relationship between 4 families.S1♂×Z3♀ and S6♂×Z22♀ were clustered together firstly because of the nearest genetic relationship(0.089 6),and then clustered with Z7♂×J26♀.J5♂×Z19♀ was not clustered into any clade because the phylogenetic relationship between J5♂×Z19♀ and other families were more distant(0.120 1-0.125 4).Additionally,of all 506 detected bands,40 family-specific bands were found to distinguish the four families from each other.Therefore,superior family could be selected from optimum breeding pairs of high level of genetic diversity which would be good for genetic improvement of T.granosa,by analyzing genetic structure of reproductive families.