Extracted and purified by using fractional precipitation, as contrast with same stage diploid, the vitellogenin cytochemistry allocation of triploid rainbow trout was made by detecting gonad, liver, blood and intestines at different developmental stage with immunohistochemical method. The testing result showed that: The purified protein was a kind of Vitellogenin, showing peculiar female. The vitellogenin were not measured in the examined organizations of tiploid rainbow trout atⅠ-Ⅴstage. The reaction of the vitellogenin were positive in blood and liver of female diploid rainbow trout at Ⅲ stage, and in ovaries at Ⅳ-Ⅴstage Vg, but it was negative reaction in bowels atⅠ-Ⅴstage. The ectogenic vitellogenin of diploid rainbow trout was produced in the liver of mature female, under estrogen′s control, before being secreted into the bloodstream and later incorporated into growing oocytes. The liver of triploid rainbow trout can not synthesize adequacy vitellogenin which was necessary to oocytes development; this was one reason that the triploid female rainbow trout was sterile.