This paper focuses on the efficiency issue of single-stage magnetic reluctance coil transmitters under loose coupling conditions, and systematically studies the influence mechanism of armature shape on transmission efficiency. By combining theoretical modeling, numerical simulation and experimental verification, the influence of armature structure on transmission efficiency is systematically studied. Through finite element simulation and experimental verification, the magnetic field distribution, force characteristics and energy conversion efficiency of cylindrical and annular armatures under loose coupling conditions are compared and analyzed. The research results show that the annular armature has the best transmission efficiency under the same loose coupling conditions due to its significant magnetic field focusing effect, which is about 10% higher than that of the cylindrical armature. The radial size gradient of the armature structure is positively correlated with the magnetic field coupling strength, which is the core factor affecting the efficiency. This study provides theoretical support and experimental basis for the optimization design of armatures in loose coupling magnetic reluctance transmitters.