When hypersonic flight vehicle flies in near space region, the strong friction between vehicle and air leads to the ionization of air. Thus, plasma sheath surrounding the vehicle and wake flow fields behind are formed, significantly affecting the electromagnetic (EM) scattering characterization of the vehicle and resulting in the communication blackout. Therefore, the investigation of electron density distribution of the plasma sheath and wake flow field is of the great significance for the detection, communication, etc. of the hypersonic target. In order to meet the requirements of on-ground electron density distribution measurement of the transient plasma flow fields, the feasibility of measuring electron density profile with seven-channel microwave interferometer measurement system is demonstrated in this article. The wake plasma is modeled as a non-uniform multilayer medium, and the full-wave simulation software FEKO is used to calculate the phase-shift information of EM wave transmitting through non-uniform single-layered dielectric plate, uniform and non-uniform multi-layered dielectric plates. According to the simulation results, the dielectric constant of the substrate is retrieved and compared with the preset results. The retrieved results show that it is feasible to measure the dielectric constant distribution of non-uniform multi-layered dielectric plate utilizing the proposed microwave interferometer system with one transmission port and seven receptions. The amplitude-phase dynamic range analysis of the proposed Ka-band microwave measurement system is also demonstrated. The key technologies including large instantaneous amplitude-phase dynamic range and ray tracking inversion algorithm for two-dimensional (2-D) electron density distribution are also solved. Finally, the complete scheme of Ka-band seven-channel microwave interferometer measurement system is introduced. The system includes one lens antenna to generate the required plane wave and seven open-ended waveguide receiving antennas which are asymmetrically arranged to improve the lateral spatial resolution of the system. The system exhibits amplitude and phase dynamic ranges of over 65dB and 180° under 1 MHz IF bandwidth respectively. The plasma electron density distribution measurements utilizing the proposed seven-channel microwave interferometer system are carried out on the ballistic range and multi-functional shock tube. The response time of the system is smaller than 1μs, satisfying the requirement of the two-dimensional distribution measurement of the transient plasma flow field generated by the ballistic range and multi-functional shock tube. The differences between experimental and numerical results are less than 0.5 order of magnitude and the variations in transient plasma generated in both ballistic target and shock tube equipments were well detected. The measurement range of plasma electron density is 10¹⁰-10¹³ cm^-3 and the spatial resolution is better than 15mm. In addition, the proposed ray tracing method is also used to invert the 2-D electron density distribution of both square and cylindrical layered models under identical experimental state. The results are in consistent with each other, indicating that the proposed ray tracing method can be applied in the inversion of 2-D electron density distribution of plasma with different shapes.