Abstract：Groundbased dualfrequency GPS receiver has been widely used to monitor the ionosphere and its related abnormal activities. In the past time, however, it was often used by establishing a 2D groundbased GPS ionospheric grid model, which ignores the vertical ionospheric information taken as a constant. 3D ionospheric electron density profile is obtained through a Multiplicative Algebraic Reconstruction Technique (MART) using groundbased GPS measuremnts. Comparied with the International Reference Ionosphere2001 (IRI2001) and ionosonde, the ionospheric electron density profiles derived from ground-based GPS tomography are almost consistent, but much closer to that obtained by ionosonde. Therefore, the groundbased GPS with high timespace resolutions plays an important role in monitoring 3D ionopsheric activities and related space weather.\
