Magnetic induction (MI) communication has the characteristics of being less affected by the medium and having a stable channel, which can effectively solve the problem of excessive transmission loss of electromagnetic wave (EW) communication in extreme environments. However, as a near−field communication technology, the limitation of its near−field effective range leads to the restricted coverage of magnetic induction communication. Therefore, in−depth research on the magnetic induction boundary is of great significance for guiding the design and optimization of magnetic induction communication systems. This paper studies the spatial distribution of the electromagnetic field of a thin ring antenna in free space, comprehensively considers parameters such as antenna size, and proposes a decision parameter to give a stricter magnetic induction boundary. On this basis, the range of ring parameters under different frequencies and spatial angles is determined through error analysis, providing theoretical support for the parameter design of magnetic induction communication. By analyzing the variation laws of three verification parameters, namely the amplitude of wave impedance, the phase difference between the spatial electric field and magnetic field, and the spatial variation rate of the magnetic induction receiving intensity factor, with distance, the physical characteristics at the magnetic induction boundary are deeply revealed. The research finds that at the magnetic induction boundary, the magnetic field energy is dominant, the electromagnetic field distribution has not yet reached a stable state, and the physical property of rapid attenuation of the magnetic induction receiving energy is presented. Simulation results show that the proposed magnetic induction boundary formula can accurately describe the magnetic induction limit distance and ensure the effective performance of magnetic induction communication within the boundary range.