To study the change of reproductive system in morphology and tissue structure of imposex of H.tuba and the possible adverse effects on the populations of Hemifusus tuba,this experiment studied the reproductive system structure of immature and mature,normal and imposex of H.tuba collected from Zhanjiang,Beihai,Qinzhou,Fangchenggang in China and Ho Chi Minh City in Vietnam along the coastal waters of Beibu Gulf by the methods of anatomy,histology and SEM.In this paper,we described anatomical and histological structures of imposex genital system of H.tuba for the first time.The results showed that the imposexed females exhibited a penis and/or vas deferens in addition to the normal female genital organs.Moreover,the penis location,shape and tissue structure of vas deferens in the imposexed females are similar to the normal males.We found that the imposex phenomenon only occurred in mature H.tuba,and the gonadogenesis was blocked in high degree's imposexed females.All the results indicate that the imposex order of severity in H.tuba from IOI is Beihai 1>Beihai 2>Zhanjiang>Qinzhou 1>Fangchenggang offshore>Ho Chi Minh City,Qinzhou 2 and Fangchenggang White Dragon Pearl Bay.Especially,the imposex is the most serious in Beihai populations,the imposex rate is 90% on average,and it is also higher than the other populations in VDSI.What is more,the sex ratio index of H.tuba in Beibu Gulf is almost all less than 1,and presents a decreasing trend in general.Therefore,imposex induced by TBT may result in population decline of H.tuba in Beibu Gulf by disrupting the female reproductive mechanism.