Abstract: The statistic variation of horizontal magnetic field measured by the DEMETER satellite in the ELF (3—30 Hz) and SLF (30—300 Hz) range is compared with the atmosphere noise measured on ground. The difference between DEMETER and ground observations accords with the law of radiowave propagation. Therefore, it indicates that the electromagnetic field measured by the DEMETER satellite originates from the earth ground. Then, the normalized wave impendence of ELF/SLF measured by the DEMETER satellite is profoundly analyzed. The normalized wave impendence calculated from the electron density and ion density is quite different from the value calculated from electromagnetic field measurement. The present data is not self-consistent, and some problems need to be further studied.