To study modeling methods and estimation strategies for regional ionospheric Total Electron Content (TEC), a detailed introduction to the spherical harmonic function model under the single-layer ionospheric sphericalshell assumption is provided, and using data from five monitoring stations in the Xi’an region, regional ionospheric modeling was performed using three-order spherical harmonics. Verification demonstrated that for single-frequency users, the User Range Error (URE) obtained using the regionally modeled ionosphere based on spherical harmonics is 0.79 m (1 σ), with horizontal and vertical positioning accuracies of 1.76 m and 2.41 m respectively. Compared to using the Global Ionosphere Map (GIM) model, the represents improvements of 56.83%、56.86% and 62.40% respectively. The ionospheric delay correction effectiveness was markedly improved.