The hyperelastic stress-strain constitutive model of the gastrointestinal tissues is introduced. According to the special characteristics of the gastrointestinal biomechanism, a locomotion gait based on anchoring-extending is proposed for the gastrointestinal micro robot. The relationship between the speed of single cabin and the resistance force is established through studying the mechanical interaction between single cabin of the micro robot and the intestinal tissues, and the locomotion efficiency of the robot is established through studying the mechanical interaction between the entire robot and the intestine. A critical step model based on the hyperelastic constitutive model is deduced based on the above mechanical analyses. This model is a guide for robot design and parameter optimization. Finally, the relationship between the robot's single cabin speed and the tension force is obtained through robot model experiments, and the critical step model is verified in an in-vitro
experiment with a robot prototype.