A miniature intestinal anchoring mechanism is designed to realize the effective anchor of a gastrointestinal robotic endoscope in the special environment of human intestine. The mechanism explores a kind of expansion method through protruding three sets of legs radially, which lowers the risk of intestinal clamping because the three sets of legs show a enclosed structure after expansion. At the terminal of every legs, a curved plate is fixed to enlarge the contacting area between legs and intestine, which reduces the damage to intestinal tract. The interaction between anchoring mechanism and intestinal tract is modeled. The anchoring force is divided into two parts, Coulomb friction and marginal resistance, and its mechanism is analyzed. The expanding force and anchoring force are tested through experiments. The experimental results show that the expanding force of the anchoring mechanism is close to the theoretical analysis, and the anchoring force is related to intestinal diameters, the expanding diameters of anchoring legs and the speed of the anchoring mechanism. When the diameters of the anchoring legs are 20—26 mm, the anchoring force is 0.15—0.4 N;when the diameters of anchoring legs are greater than 26 mm, the anchoring force increases rapidly between 0.5 N and 1.8 N. The anchoring mechanism proposed in this paper is characterized by safe and a smaller volume and is suitable for the physical environment of the intestine. It provides a new idea for design of the intestinal anchoring mechanism for micro robots in gastro intestinal tract diagnosis.