The Decapodal, Copepoda, Cladocera and Ostracoda taxonomy are the popular species of crustaceans in freshwater in general, and in the water bodies of karst in particular. The biodiversity of these groups is reflected in the abundance of the species, number of individuals and distribution in the community. They play a major role in the food chain and food net of aquatic ecosystem. Many species are economically exploitable. In the world, many studies on the fauna in general and the freshwater crustaceans in the water bodies of karst in particular, including cave underground water were realised with interestingly results which many new genus and species have been found. In Vietnam, for the topographical karst in general and the limestone mountains of Phong Nha-Ke Bang National Park in Quang Binh Province in particular, especially for underground water bodies in the cave underground water bodie there are very few research on biodiversity characteristics, species composition of the aquatic fauna in general and the crustacean group in particular. Previous studies on the environment and aquatic life in the Phong Nha-Ke Bang National Park have recorded 33 freshwater crustacean species, of which 12 species are found in the Phong Nha cave. Of the species found in the river in the Phong Nha cave, two new Calanoida crustacean species for science are described. These new species and genus are currently being considered endemic to Vietnam. Certainly, these above results have not fully reflected the species composition and distribution characteristics of freshwater crustaceans in the topographical karst, espcially the cave underground water in the karst of Phong Nha-Ke Bang. Therefore, we propose the research topic: “Study on species composition and distribution characteristics of freshwater custacean in water bodies of Phong Nha-Ke Bang National Park”.