Abstract: Abstract:Characteristics of the average power spectrum density (APSD) are studied using the data of electric field observed by DEMETER satellite.The study area covers China and its adjacent regions(0deg;mdash;60deg;N, 60deg;Emdash;140deg;E), and the time period ranges from January 1, 2008, to September 12, 2008. The observed data during the days with average Kp index smaller than or equal to 4 were selected for analysis. Spatial distributions of dayside and nightside APSD with 16 day period were mapped for LF (10mdash;20 kHz) and MF (20 kHzmdash;3 MHz). We obtained the following preliminary results. For LF: ① Spatial distributions of dayside APSD in the same period and at different frequencies show poor similarity in pattern and are characterized by latitudinal zonation, while those of nightside APSD display good pattern similarity, with main difference only in amplitude and without clear zonation. ② The range of amplitude variation of dayside APSD is much smaller than that of nightside APSD, the former being generally in 1mdash;1.5 orders, while the latter varying beyond 2 orders and even up to 4 orders. ③ The APSD near Chengdu-Lanzhou changes clearly before and after the 2008 Wenchuan earthquake.For MF: ① Spatial distributions of dayside APSD in the same period and at different frequencies show no similarity, and the distributions in different periods and at the same frequency may have good, poor or no similarity and may show clear, poor or no zonation. While the distributions of nightside APSD in the same period and at some frequencies display very good pattern similarity. Good similarity can be seen in the nightside APSD patterns deduced from data in different periods and at the same frequency, but no latitudinal zonation or only weak longitudinal zonation can be found. ② Amplitude variations of both dayside and nightside APSD are not significant, being generally less than 0.5 orders. ③ The APSD near Chengdu-Lanzhou did not show clear changes before and after the 2008 Wenchuan earthquake.