In eddy current testing (ECT), a thin-opening crack in a plate conductor is much frequently encountered. The eddy current field perturbation due to the crack may be described as the effect produced by an equivalent current dipole layer located on its surface. The dipole density may be found by solving a boundary integral equation. In this paper, formulas of the electric dyadic Green's function for a limited thickness plate are derived. Following a moment method scheme, numerical predictions are made for Benchmark models of ECT for steam generator, step 2. The eddy current perturbations due to the cracks are calculated. The probe impedance changes are also evaluated and are compared with experiments, and good agreement is found.