Because of continuous covering, the Geostationary E arth Orbit (GEO) satellites play an important role in GNSS constellations like BDS. The advantage of using GEO satellites to monitor the ionosphere is the almost motionless ionosphere pierce point (IPP), which is analyzed by comparison with ME O and IGSO satellites. The results of observation data analysis using several tracking stations show that the VTEC sequence derived from each GEO satellite at their respective fixed IPP is always continuous. The precision of calculated VTE C using BDS B1&B 2, B1&B3 and B2&B3 dual-frequency combination was compared and analyzed. The VTE C12 precision based on the carrier phase and code is 0.69 TE CU and 5. 54 TE CU, respectively, which is slightly higher than VTE C13, and much higher than V TEC23. Furthermore, the ionosphere monitoring results were obtained at selected stations in northern hemisphere, near the equator and in southern hemisphere respectively. The long-term variations of the correlation between the ionosphere and solar activity were analyzed, and the short-term variations of the correlation bet ween the ionosphere and the DS T index were analyzed.