The issue of a high line failure rate due to long transmission distances is faced by the UHV three-terminal hybrid DC transmission system, which is an important form of DC transmission. The basis of stable system operation is formed by accurate fault location. A fault location method was proposed that addressed the challenge where existing fault location methods were applied to the unipolar grounding fault of the transmission line, leading to issues of fuzzy location and low accuracy under high resistance grounding fault conditions. The method proposed using wavelet packet entropy feature fusion to extract fault features and employed a BiTCN model optimized by ISSA. Firstly, the line-mode voltage traveling wave signal was extracted using wavelet packet transform, and the deep fault characteristics in the voltage waveform were described using information entropy. The feature matrix, composed of the entropy feature fusion feature vector, was formed as the input of the BiTCN model. Secondly, the BiTCN model was constructed and trained, and it was optimized using iterative ISSA optimization. Finally, accurate fault location of the three-terminal hybrid DC transmission line was achieved. The feasibility of the proposed method is verified by constructing the system model in the PSCAD/EMTDC simulation platform. The results indicate that the method is characterized by high positioning accuracy, good generalization ability, and robustness, and high resistance faults are effectively tolerated.