Abstract: Based on in-situ plasma parameters observed by plasma analyzer (IAP) and Langmuir probe (ISL) of French DEMETER satellite, we studied 5 methods for anomaly extraction, i.e., variation of parameters with latitude, spatial interpolation, spatial difference, moving median and correlation analysis. The methods were applied to the study of 29 earthquakes from Jan. 2006 to Apr. 2010, including the M≥6.0 earthquakes in China and some M≥7.0 earthquakes worldwide. As the plasma parameters are correlated to a certain extent, when 2 or more parameters show abnormalities, they are accepted as disturbances before earthquakes. In-situ plasma parameter abnormalities were found before 15 of the 29 earthquakes. Through analysis we noted that the abnormal time was usually from 1 to 7 days before earthquakes, and the abnormal regions might appear both to the east and west of the epicenters, mostly leaning to the magnetic equator.