Abstract: The main phenomenological features of ionospheric precursors of earthquakes are introduced firstly, and the ionospheric scale height estimation method at the height of maximum electron density is studied by the constellation observing system for meteorlogy, ionosphere and climate (COSMIC)occultation data products. Then, the anomalous changes of ionospheric parameters before Eastern Japan Great Earthquake happened on Mar 11,2011 are analyzed based on comprehensive observed data from the ground based ionosonde, GPS and spaceborne GPS occultation. It is shown that several ionospheric anomalies appeared three days before the earthquake, including that ionospheric f0F2 and relative vertical total electron content (VTEC)existed anomalous disturbance, and ionospheric Hs increased. After we analyze the impact of geomagnetic activity and solar activity, we think that all the results are related to Eastern Japan Great Earthquake. It is demonstrated that ionospheric anomalous changes can offer important information for the short-term earthquake prediction.