This paper r eported the observat ion about “crack shell disesae” of cul tur al abalone baby by microscope and elect ronic microscope .The symptoms are as f ollows :the shell is thin , the edge is turndowning , the hole is l inking , the absor bing abilit ies decrease , and the growing rate is much low.The pathogen is a kind of spher ical vir ion which was determined by observat ion and art ificially infected e xperiment .The virion mainly invaded the blood cells .This studies also observed the histopathological changes of mant le , feet , gill , l iver and crop and pointed out the inf ection-like ch ange appeared in epidermis and connective tissue cells of main organ and the ult rast ructure changes is the mitochondr ion expansion , the r idge disappe ar ing , and the e ndoplasm disintegr ating .The necrosis of digestive, r espir e and move organs accele rated the death of the abalone .The infect ing ch annel is horizontal .Meanwhile the pathogenic characters were discussed .