A brand new magnetic untethered peanutlike millirobot (MUPM) was created with two different motion modes—rolling motion and crablike motion, and designed to be actuated under a rotating magnetic field generated by a magnetic driving navigation system (MDNS). The dynamic characteristics of the MUPM in the different motion modes were studied through modeling. By adjusting the frequency of the rotating magnetic field, the movement velocity of the MUPM could be controlled and motion mode switching initiated, while the direction of the motion was controlled by regulating the rotating magnetic field direction. The mechanism of motion mode transitions was then analyzed and simulated. The MDNS allows the MUPM to navigate along a preset trajectory from a starting point to a destination, and tracking-learning-detection (TLD) algorithm achieved accurate tracking of the MUPM. It was demonstrated that the MUPM has excellent maneuverability in both its motion modes and can pass through a narrow channel to a targeted area by switching modes. The obstacle-overcoming ability of MUPM in two motion modes is tested. The MUPM is expected to have great application value in the field of targeted intraluminal drug delivery.