The bridge local scour monitoring is characterized by adverse environment with great danger which makes sensor arrangement very difficult. So, we proposed using magnetic label rock as a dynamic scour sensor for bridge scour monitoring. The monitoring system consists of magnetic label rock and magnetic gradiometer. The magnetic label is casted into concrete to construct a magnetic label rock. The degree of freedom is reduced to solve the nonlinear and ill-posed problems in the magnetic reversion by means of optimization search. In the experimental verification for localization of magnetic label rock, the maximum error and relative error for localization is about 0.2 m and 5% respectively, which satisfies the requirement in the bridge local scour monitoring. The magnetic gradient, invariants and magnitude are all highly correlated with scour displacement, which can be directly used for early warning in the bridge local scour monitoring.