For the space omnidirectional wireless power transmission technology and system, a flat D-core structure is proposed in this paper. By comparing the characteristics of various current soft magnetic materials, a suitable core material is selected. According to the simulated magnetic field distribution characteristics of the core in various attitudes, the receiving coil is designed as the combination of three sets of orthogonal and independent coil structures, and the influence of structural parameters, such as the width and thickness of the core, on the performance of the coupling mechanism is analyzed. Finally, the equivalent mutual inductance between the coupling mechanism proposed in this paper and the existing coupling mechanism with similar structure is analyzed and compared by means of simulation and experiment. The output characteristics of the omnidirectional wireless power transmission system based on the coupling mechanism are tested, and the results show that the equivalent mutual inductance value of the coupling mechanism proposed in this paper is greater than the existing mechanisms under the same conditions.