At present, due to the complex structure of multi-segment and multi-branch, there are problems of long time-consuming and low efficiency in line grounding fault location. Taking a typical complex distribution network area as an example, the grounding fault rate reached 10 times/100 kilometers in the past year, and the traditional location method took about 25 minutes on average. When the traditional binary particle swarm optimization algorithm is applied to this scene, it is easy to fall into local optimization and global optimization is limited because of the lack of constraint of speed update mechanism. Moreover, the single fitness function of other methods can not give consideration to both accuracy and efficiency, which leads to insufficient positioning accuracy and is difficult to meet the actual needs. Therefore, this paper proposes a method of cross-domain line grounding fault location in distribution network based on improved binary particle swarm optimization. Firstly, the fault criterion is established by constructing the distribution network operation topology based on directed graph, and the regional location of cross-domain line grounding fault is realized. Then, an improved binary particle swarm optimization algorithm is proposed on the basis of regional positioning. By introducing a dynamic adaptive Sigmoid function to dynamically limit the particle motion speed, the negative influence of particle local saturation on the global optimization result is effectively avoided. At the same time, a dual fitness function is constructed based on the fault area information, in which one fitness function focuses on improving the positioning accuracy and the other focuses on the convergence speed of the algorithm, thus significantly improving the search efficiency while ensuring the positioning accuracy. Finally, the effectiveness of the method is verified by experiments. The experimental results show that the average error of the improved binary particle swarm optimization algorithm is about 2.5m, which is 34.2% lower than that of the traditional PSO, and it can be effectively applied to the location of grounding faults in distribution networks, providing support for the operation and maintenance of power grids and safe and stable operation.