Abstract: The ionospheric electron content (TEC) is greatly affected by solar activity. When the magnetic storm occurs, the TEC changes vary widely in the world. It is very important to study the variation of TEC perturbation in this period for the study of the ionosphere.According to the inverse relationship between the ionospheric delay of the GNSS signal and the square of the signal frequency, the total electron content TEC change on the signal propagation path can be obtained. Without considering the absolute value of the TEC, the high-precision relative TEC can be obtained by using the carrier phase L4 combination, which is used to detect ionospheric disturbances. In this paper, the disturbance characteristics of the giant magnetospheric storm in March 2015 are studied by using GNSS TEC data including Beidou system and f_oF2 data of ionospheric altimeter in China, and its possible physical mechanism is discussed.