The genetic diversity of Hydra robusta was studied by RAPD technique from 17 populations of 10 distribution areas in Heilongjiang Province. Nineteen primers were selected from 80 random primers, and yielded a total of 320 bands ranging from 0.3-3.0 kb, 299 (93.44%) of which were polymorphic. The result indicated high level of genetic diversity in this species. The values of genetic identity (GI) and genetic distance (GD) of those populations were 0.7158 and 0.3425 on average, respectively. GD within distribution areas (0.1695) was lower than that between (0.3425). Cluster analysis showed that GDs of populations were consistent with their geographic distances. The population of Hutou had a clearly lower genetic identity with others (GI=0.5413 and GD=0.6161 on average) and was considered a relatively specialized one.