The rapid three-dimensional (3D) localization of γ-ray sources using Compton cameras has important application value in nuclear safety monitoring, nuclear emergency response, and nuclear facility decommissioning. To solve the problems of heavy computational burden and long reconstruction time in conventional 3D reconstruction methods for Compton cameras, this study proposes a fast 3D localization method for far-field radioactive sources based on the vector intersection with dual partition (VI-DP) method. In this method, the voxel traversal in the 3D imaging space is first transformed into a grid search on a two-dimensional imaging plane through the vector intersection method. Based on the imaging results of the Compton camera from different viewing angles, two vectors pointing toward the radioactive source are constructed, and the spatial intersection point (or the nearest point) of the two vectors is calculated as the estimated 3D position of the source, thereby significantly reducing the computational complexity.Based on this, a dual partition method is introduced to dynamically reduce the search range on the imaging plane, and the search is performed only in regions with a high probability of containing the source, further improving the 3D localization speed. The experimental results show that the vector intersection method exhibits good 3D localization performance under different distances or deflection angles, and it can still achieve accurate 3D localization of the radioactive source at large deflection angles. Compared with the MLEM iterative algorithm, the 3D localization time is reduced by about one order of magnitude. After coupling the dual partition method, while achieving higher 3D localization accuracy, the localization speed can be improved by approximately 2-3 orders of magnitude compared with the MLEM iterative algorithm, and by about 1-2 orders of magnitude compared with the direct BP algorithm. Consequently, the VI-DP method achieves a synergistic optimization among 3D localization accuracy, imaging angle resolution, and computational effciency. This study can provide effective technical support for the rapid and precise localization of radioactive sources in relevant nuclear scenarios.