Based on the electron density (Ne) and temperature (Te) data from DEMETER, the ionospheric perturbations before 82 Ms⩾7.0 earthquakes (EQs) during 2005–2010 were studied, using moving median and space difference methods within 10days before and 2days after these events in local nighttime. It was found that the plasma parameters disturbances appeared before 49 EQs, in which more disturbances were detected before shallow-focus earthquakes than deep ones, and there was little difference between continental and oceanic ones, both exceeding 1/2 percentage. For the disturbed time, more perturbations were seen in 1, 3, 5, 6, 8days before EQs and 1day after EQs. For the spatial distribution, the anomalies before EQs were not just above the epicenters, but shifted equatorward with several degrees to almost twenty degrees. Most of the abnormities were positive ones, which demonstrate that Ne increases before EQs at the altitude of 670km of DEMETER. Perturbations of Ne were more than that of Te, which illustrates that Ne is much more sensitive to seismic activity than Te.