Skin friction drag is a critical component of total drag for future aerospace vehicles. Reducing the skin friction drag under turbulent flow conditions is of great significance for improving the aerodynamic performance and saving energy of the vehicles. In recent years， active flow control techniques utilizing surface arc discharge plasma actuators have achieved a series of exploratory advancements in the control of high-speed boundary layers due to their simple structure， broad frequency bandwidth， and rapid response characteristics. However， detailed quantitative research on the interaction between the plasma excitation and supersonic turbulent boundary layer， which is an essential fundamental problem， remains limited. This study addresses this gap by directly solving the Navier-Stokes equations with a plasma phenomenological model. The effects on flow structures， turbulence statistics， and wall quantities of a Mach number 2.9 supersonic turbulent boundary layer actuated by a plasma at a frequency 50 kHz were elucidated. The results indicate that the plasma actuation leads to an increase in mean temperature and a decrease in mean density within the boundary layer， with an inflection point appearing in the mean streamwise velocity profile. This triggers Kelvin-Helmholtz shear instability in the outer layer of the boundary layer. Furthermore， Reynolds stresses and turbulent kinetic energy exhibit an overall reduction trend across the boundary layer in the downstream of the plasma location. Notably， the actuation achieves a maximum drag reduction rate of approximately 28.4% in the downstream region， which mainly ascribed to the decrease in the production of turbulent kinetic energy and molecular viscous dissipation. Conversely， drag enhancement is observed near the actuation， caused by adverse pressure gradients generated by precursor blast waves within the boundary layer.