Based on multiple wedge effects, this paper describes an innovative variable-diameter capsule robot with radial clearance compensation for active locomotion inside the gastrointestinal (GI) tract using an outer rotating magnetic field. The surface of the capsule robot, encapsulated by a thin latex sleeve for protecting the GI tract from any injuries, is composed of four copper tiles, on which four separated spiral blades are wound respectively. When the capsule robot rotates, its four copper tiles are extended synchronously under the action of their centrifugal forces, achieving reduced clearance between the surface of the capsule robot and the pipe inner wall, and a convergent wedge-like gap between the surface of each of four copper tiles and the pipe inner wall is formed, resulting in multiple wedge effects when fluid travels through the four convergent wedge-like gaps. The radial dynamic balance equation and kinematics equation of the capsule robot are derived according to fluid dynamics. To investigate multiple wedge effects, the capsule robot prototype with clearance compensation has been designed, manufactured, and tested. Simulations and experiments have demonstrated that the propulsion and swimming speed of the capsule robot are significantly improved, and the innovative capsule robot is capable of swimming vertically inside a pig's intestine; thus, it has a promising prospect for medical applications.