Abstract: Port selection plays a critical role in the corrosion diagnosis of grounding grids. However, the lack of scientific guidance for port selection has restricted the application of network-based corrosion diagnosis methods. To address this issue, this paper proposes an iterative optimization method for port selection based on weighted coverage and multi-weight collaborative optimization. The method firstly establishes a port scoring model using the sensitivity matrix to quantify port values from three aspects: information complementarity, information richness and numerical stability. An iterative optimization strategy is then adopted, which greedily selects ports while predicting the resistance of grounding grid branches, thereby enabling recursive correction of the sensitivity matrix and gradually screening out port combinations with high-quality information. Finally, simulation experiments conducted on a simulated grounding grid with 53 branches show that, compared with the unweighted greedy selection with the same 14 selected ports, the weighted greedy selection method reduces the mean absolute percentage error from 34.83% to 5.7%. It is verified that the proposed method can effectively optimize the measuring port selection and improve the accuracy of grounding grid corrosion diagnosis. The research conclusions can provide theoretical guidance for port selection in corrosion diagnosis of large grounding grids.