Abstract: To obtain the main parameters range of the anchoring-extending gastrointestinal micro robot, the critical step model was deduced by using the hyperelastic stress-stain constitutive model, which describes the biomechanical behavior of the intestinal tract. For extending mechanism, according to the relation factor of the speed and resistance force in the critical step model, a smooth signal cabin robot model was used in experiments, with in vitro small intestine of various diameters; for anchoring mechanism, a legged robot model was used to test the anchoring force in difference leg length. The experimental result is returned to the model to export some robot design guidelines. Finally, a robot prototype was used in an in-vitro experiment to validate the critical stroke model. Key words：

Key words: intestinal robot, hyper-elastic constitutive model, critical step, in-vitro