The invention belongs to the technical field of concrete durability monitoring. The invention particularly relates to an ECT sensor structure optimization and electromagnetic field analysis method. The technological process comprises eight steps including parameter setting, geometric setting, material setting, mesh generation, physical field setting, solving, sensor structure optimization and electromagnetic field distribution calculation. A new idea is provided for solving the positive problem of an ECT system based on software COMSOL. After modeling is completed, the uniformity degree of thesensitive field of an ECT sensor is analyzed through a calculation result, structure parameter values of all parts of the ECT sensor are adjusted, an optimal design scheme is searched for, meanwhile,change of the internal electromagnetic field when a concrete structure contains water can be visually and clearly observed, the relation between the internal moisture content of the concrete structure and the relative dielectric constant is obtained, the accuracy of imaging the internal moisture content of the concrete structure through the ECT technology is improved, and a new verification method is provided for the durability test of the concrete structure.