The traditional method of offline measurement of rail-to-ground transition resistance for estimating insulation degradation ranges in metros is inefficient and ineffective. To address this

this paper proposes a new rail-to-ground insulation degradation positioning method using station rail potential monitoring information to enhance diagnostic efficiency. A resistance network model of track return current system is established

and the sensitivity relationship between rail potential and rail-to-ground transition resistance is derived using electrical network sensitivity analysis. An underdetermined equation linking station rail potential deviation to rail-to-ground transition resistance is built

and an augmented equation set considering the spatiotemporal correspondence between train operation and rail potential distribution is developed. The least squares iterative calculation method is applied to compute rail-to-ground transition resistance

thus the positioning of rail-to-ground insulation degradation can be realized on the basis of safety limits. Simulations based on actual metro line conditions show that the method can be adopted to diagnose rail-to-ground insulation degradation with high accuracy

the localization accuracy is over 99% before adding Gaussian noise

and remains above 74% after adding Gaussian noise.