In order to calculate eddy current testing (ECT) signals due to a complex natural crack by using a regular mesh, the multi-media element (MME) was proposed by authors. In this paper, a new high-precision method for calculating the MME coefficient matrices is proposed and implemented in the finite-element method (FEM)-BEM hybrid code for ECT of narrow cracks. Through the comparison of the new MME solutions with those of the conventional FEM-BEM method, validity and efficiency of the new method and the corresponding numerical code are demonstrated. Eddy current perturbations and distributions of the magnetic flux density affected by a narrow crack of different directions are also numerically analyzed by using the new MME. In addition, the measurement results from the experiments give further support to the validity of the new MME method.