The development of the Koch curve fractal geometry provides valuable ideas for the structural design of sensor. Conventional eddy current sensor (CECS) cannot effectively concentrate electromagnetic fields’ energy and have low detection sensitivity. The eddy current sensor (ECS) based on the Koch curve fractal geometry can change the distribution of electromagnetic fields in space. Therefore, based on the Koch curve fractal geometry, a novel ECS with multiple spatial degrees of freedom (SDOFs), including torsion structure of the $xy$ plane and inclination angle of the $yz$ plane, for concentrating magnetic fields (MSECS) is developed in this article. The proposed multiple SDOFs are analyzed and optimized by finite element analysis. An energy spectrum function is proposed to describe the distribution of eddy current. The simulation results show that MSECS can concentrate electromagnetic fields and improve energy transfer efficiency. Defect detection experiments are conducted on prefabricated defective steel plates, which show that MSECS has a better performance of detection.