ChEss is a pilot project within the Census of Marine Life (CoML) initiative. The main objective of ChEss was to determine the biogeography and biodiversity of deep-water chemosynthetic ecosystems and to understand the processes driving them. Chemosynthetic ecosystems include hydrothermal vents, cold seeps, whale fall and other highly reduced ecosystems. To assess the biogeography and biodiversity of chemosynthetic ecosystems it is essential that all the above systems be studied in combination. Determining the evolutionary and ecological relationships among their fauna is crucial to understanding the processes that shape the distribution of species from chemosynthetic ecosystems at the global scale. The background, content, goal, research area, technique, methods, progress and future plan are introduced in this paper, which is expected to be useful for the study of biodiversity and biogeography in deep sea chemosynthetic systems and other extreme environment in China.