In the last 10 years, jellyfish bloom occurred in the ocean globally, especially in the coastal waters. Jellyfish bloom is one of the main ecological disasters in the ocean; it affects the coastal industries, fishery and tourism. It is one of the worldwide issues to understand the causes, mechanism and consequences of the jellyfish bloom. The big challenges for the jellyfish bloom research include jellyfish bloom observation, absence of the long term data, complexity of the life cycle for many of the jellyfish. The jellyfish bloom is an indicator of the marine ecosystem change; it is one of the ecosystem responses to the global climate change and the human activities.