  To better understand magnetic structure and eruptive process of solar
filaments, a solar active-region filament (labeled F2) eruption associated with
a B-class flare was investigated by using high-resolution H$\alpha$ data from
the 1 m New Vacuum Solar Telescope (NVST), combined with EUV observations of
the Solar Dynamical Observatory (SDO). The filament F2 was disturbed by another
filament (labeled F1) eruption that experienced a whip-like motion. Before the
filament F2 eruption, the Dopplergrams show that the southern and the northern
parts of the filament F2 body exhibit blueshift and redshift along the filament
spine, simultaneously. It implies that the filament F2 was rolling from one
side to the other. During the filament F2 eruption, the Doppler velocity shifts
of the filament body are opposite to that before its eruption. It demonstrates
that the filament body exhibits an untwisting motion, which can be also
identified by tracing the movement of the eruptive filament threads. Moreover,
it is found that the material of the filament F2 was transferred to the
surrounding magnetic field loops, which is caused by magnetic reconnection
between the filament F2 and the surrounding magnetic loops. According to the
right-bearing threads of the filament F2 before its eruption, it can be deduced
that the filament F2 is initially supported by a sheared arcade. The following
observations reveal that the twisted magnetic structure of the filament F2
formed in the eruption phase.
