Abstract: In order to study the electromagnetic characteristics of the plasma sheath around hypersonic aircraft in High-Frequency Plasma Wind Tunnel,a new Langmuir probe system has been developed in this paper.High-Frequency Plasma Wind Tunnel is ideal facility for the re-search of electromagnetic characteristics of the plasma sheath,and electron density,electron tem-perature and their distribution is very important to the researching test.In this probe system,the high performance molybdenum probe and adjustable power device have been manufactured.By this probe system,the test principle and data processing method are discussed,the electron densi-ty and its change rule of core area for wind tunnel with different operating power and different gas flux are measured.At the same time,the electron density radial distribution is measured with the same operating power and gas flux.Moreover,the test results have been compared with the mi-crowave means data.It shows that this electrostatic probe system can meet diagnostics of flow field parameters in high frequency plasma wind tunnel well,and can provide reliable data to sup-port the numerical simulation of wind tunnel flow field and electromagnetic characteristics study of plasma sheath.