Solar filament eruptions are often associated with solar flares and coronal mass ejections, which have the greatest impact on space weather. However, the fine structures and the trigger mechanisms of solar filaments are still unclear. To address these issues, we studied a failed solar active-region filament eruption associated with a C-class flare by using high-resolution H images from the New Vacuum Solar Telescope, supplemented by EUV observations from the Solar Dynamics Observatory. Before the filament eruption, a small bipolar magnetic field emerged below the filament. Then magnetic reconnection between the filament and the emerging bipolar magnetic field triggered the filament eruption. During the filament eruption, the untwisting motion of the filament can be clearly traced by the eruptive threads. Moreover, the footpoints of the eruptive threads are determined by tracing the descending filament material. Note that the twisted structure of the filament and the right part of the eruptive filament threads cannot be seen before the filament eruption. These eruptive threads in the right part of the filament are found to be rooting in the weak negative polarities near the main negative sunspot. Moreover, a new filament formed in the filament channel due to material injection from the eruptive filament. The above observations and the potential field extrapolations are inclined to support the idea that the filament materials were transferred into the overlying magnetic loops and the nearby filament channel by magnetic reconnection. These observations improve our understanding of the complexity of filament eruptions.