A trajectory-corrected rocket projectile with an isolated rotating tail rudder provides a new concept for a low-cost trajectory correction and guidance due to its simplified guidance principle. To study the angular motion characteristics of a trajectory-corrected rocket projectile with an isolated rotating tail rudder under the action of a periodic control force, the angular motion differential equation described in the complex plane is derived based on the rigid body trajectory equation. Furthermore, the effects of the initial conditions, gravity, and an asymmetric tail on the flight stability of the projectile in an uncorrected trajectory state are studied. The critical rotational speed of the tail rudder, which makes the projectile unstable due to the Magnus moment, and the rotational speed of the tail rudder, which causes projectile resonance, are derived. The transient and steady-state solutions of the angular motion of the projectile under trajectory correction and the variation law of the velocity direction for the projectile centroid are obtained. Finally, an example is given to verify the conclusions of this study. This research has important guiding significance for trajectory analysis, guidance control, and guidance law designs for isolated rotating rudder trajectory-corrected rocket projectiles.