Abstract: This study aims to clarify the quantitative relation between the motion of a capsule robot and the material mechanics of intestines. The "inner force friction" capsule robot (capsubot) is used as an example because it has almost the same shape as a capsule endoscope. On the basis of the theory of continuum mechanics and the five-element model, a dynamic equation is established for the capsubot's movement within intestines. The parameters of this model that are adopted in this study are obtained from our previous study. Finally, the motion effect, which is altered when the driving force is used to start the capsule, is explained quantitatively and intuitively as a "velocity-displacement" phase.