  We explore the rotational feature of deformed halos by performing the angular
momentum projection (AMP) on the ground state wave functions obtained from the
deformed relativistic Hartree-Bogoliubov theory (DRHBc) in continuum. The
DRHBc+AMP approach self-consistently describes the coupling between single
particle bound states and the continuum not only in the ground state but also
in rotational states. The rotational modes of deformed halos in $^{42}$Mg and
$^{44}$Mg are investigated by studying properties of rotational states such as
excitation energy, configuration, and density distribution. Our study
demonstrates that the deformed halo structure persists from the ground state in
the intrinsic frame to collective states. Especially, the typical behavior of
shape decoupling effects in rotating deformed halo nuclei is revealed.
