Abstract: To understand the situation of snail distribution and to explore the criteria of suscep-tible zones of schistosomiasis in endemic areas around Poyang Lake, a total of 1222910 mu of marshland in lake regions were surveyed for three years from 1982 through 1984 by 400 skillful observers. This article reports the relation between mean density of infected snails and incidence of acute schistosomiasis in marshland. We divided all susceptible marshlands of Poyang Lake area into three types, and found that about one fourth of the area belongs to the first type of susceptible zones, i.e., with high risk to schistosomiasis infection. Longitudinal observation showed that the types of susceptible zones changed very little unless measures of schistosomiasis control were taken.The results of field study suggested that we should put stress of schistosomiasis control on the first type of susceptible marshlands of Poyang Lake in future.