As a part of MIS (Minimally Invasive Surgery), endoscope plays an important role in the field of diagnosis and treatment. To combine a miniature robot with an endoscope is a new dimension in the field of medical robotics in recent years. Overcoming the shortcomings of the traditional endoscope, robotic endoscope applies new materials and technologies to the design of endoscope and booms the development of new type of endoscope. This paper compares the traditional endoscope system with robotic endoscope system and discusses the human intestine--working conditions for the robotic endoscope system in detail. The design requirements of the robotic endoscope system are put forward. An earthworm based robotic endoscope system is introduced and the structure and locomotion mechanism analyzed in detail. Though the running of robot is good, there are still some problems, such as heat generation and locomotion mechanism on the inner intestinal surface, which need to be solved.