The ionosphere can affect the phase of spaceborne Synthetic Aperture Radar(SAR) signal, which will degrade the quality of SAR imaging, especially for the low frequency wideband spaceborne SAR. Based on Advanced Land Observing Satellite-2(ALOS-2) SAR data, the ionospheric Total Electron Content(TEC) distribution is estimated by using the split-spectrum method in order to eliminate the impact of ionosphere. Firstly, the accuracy of the split-spectrum method for retrieving ionospheric TEC is validated. Then, the two-dimensional ionospheric TEC distribution is obtained based on the split-spectrum method using ALOS-2 data. The range resolution cell effect is also analyzed. The ionopheric TEC estimation accuracies of the split-spectrum method for three different typical areas in SAR image are compared. The results show that the split-spectrum method is robust to estimate the two-dimensional ionopheric TEC effectively. The range resolution cell and different scenes in SAR image also affect the TEC estimation accuracy of the split-spectrum method.