As the efficient clamping of a capsule endoscope in an intestine plays a major role for its stopping and movement in the intestine, this paper investigated and designed a kind of clamping mechanism for the capsule endoscope. Firstly, the influence factors of clamping force were discussed on the analysis of the friction and stress force of the intestine, then a clamping mechanism of Archimedean spiral legs was designed in consideration of the security of the intestine. A test platform was built to measure the clamping force of mechanism by comparing the different diameters, widths, textures and shapes. On the basis of the analysis of test result, an equation of clamping force was established. Finally, the safe control of clamping mechanism was implemented by a current feedback and the safety and reliability of Archimedean spiral legs were proved. Experimental results indicate that the optimized clamping mechanism would be 1.486 N. It can satisfy the anchoring requirements of expanding intestine and assuring the safety of colon.