In this paper, the aerodynamic coefficients of a microspoiler for a spin-stabilized projectile are studied using a computational fluid dynamics (CFD) simulation. To guarantee an effective study, the CFD simulation methodology is validated by the current literature and a wind-tunnel test. As a result, the additional axial force coefficient, additional normal force coefficient, and normal moment coefficient are obtained and varied with a wide range of Mach numbers (from 0.6 to 2.0), angles of attack (from 0 to 30°), and aerodynamic roll angles (from 0 to 180°). The numerical simulation results show that, in addition to the freestream Mach number and the angle of attack, the effect of the aerodynamic roll angle on the additional axial force and normal force coefficients cannot be negligible. By observing and analyzing a series of pressure field plots around the uncontrolled and controlled projectiles, some important phenomena are reasonably discussed. It was found that the complicated variation in the aerodynamic coefficients of the microspoiler is induced by flow modifications, such as the pressure distribution around the projectile. The results of this research are expected to be supplementary to those concerning the aerodynamic characteristics of spin-stabilized projectiles with microspoilers, as concluded in the current literature.