Plasma characteristic is studied under conditions of microwave discharge in air with the microwave diagnostics technology. The plasma is cold, weakly ionized, no-uniform and collision with S band high power microwave. The transmission waveform with 9-15 GHz continuous wave passing the plasma region and pressure of 300 Pa is obtained and normalized. A discussion on the effect of various plasma parameters on transmitted power is presented. A parabolic plasma density profile is assumed across the Epstein Profile Model. The maximum plasma electron density is obtained by transmission waveform of various frequency. Characteristic study of microwave passing through the strong collision plasma provides significant technology support to applications of stealth technique and information blockage.