Abstract: In order to use microwaves to detect brain activity, the simulation experiment and safety in brain activity microwave detection are analyzed and studied. The mechanism of brain nerve activity detection based on microwave transmission method is introduced. In the three-dimensional electromagnetic simulation software—Sim4life, combined with high-precision human head model, the effect of the change of the permittivity of the brain gray matter on the transmission coefficient is analyzed. The simulated tissues which the electrical parameters are similar to those of the head is prepared. In addition, using an on-body matched antenna and simulated tissue, a simulated experimental platform for the brain nerve activity detection is constructed. In the case of implanting simulated tissue samples with different dielectric constants, the change of S₂₁ is measured on transmission system. The simulation and experiment results show that the phase change of the transmission coefficient will increase with the increase of the change in the dielectric constant of the gray matter. Therefore, the phase of the transmission coefficient can be used as a characterization of brain nerve activity detection by the microwave. Finally, according to the SAR analysis, the limit of the transmit power of the transmitting antenna is given.