Abstract: To measure the thin plasma layer above the surface of the moon, via using radio occultation technique and coherent radio waves of the S/X-band, dual-frequency measurements could be acquired at a given Earth-based receiving station. On the line-sight direction, the terrestrial ionosphere, interplanetary plasma and thin lunar ionosphere are mixed together, in order to investigate the relatively pure variation of ionospheric total electron content (TEC) surrounding the moon. Using the trend extrapolation method, the terrestrial ionosphere and interplanetary disturbance error influence could be eliminated, so as to estimate the fitting trend component. The TEC of lunar ionosphere is obtained about ~10-14 /m2, after subtracting this trend component from the original observation data obtained at the tracking station.