Abstract: As a major digestive and absorptive organ of humans, the intestinal tract is narrow and winding with a complicated surface structure, so complications such as tissue injuries and capsule stagnations frequently occur in the diagnosis process, which thus inspires considerable researches concerning the frictional characteristics of the intestinal tract and the capsule endoscope, which play an important part in treating the above mentioned diseases and developing harm-free endoscopes. This paper briefly reviews the categories of capsule endoscopes and outlines the frictional characteristics between the capsule endoscope and the intestinal tract, the microrobot and intestinal tract, concentrating on two aspects: (1) the researches concerning the friction reduction of the capsule endoscope, including research methods of the frictional characteristics, the relationship between the capsule structure and the frictional resistance, the researches of the frictional mechanism, the prediction model of the frictional resistance and the optimization of the capsule structure; (2) the researches of the friction increase for the realization of autonomous walking of in vivo micro-robot, including the methods of increasing frictional force and the related mechanisms. Finally, some scientific questions for further studies are raised.