To study modeling methods and estimation strategies for regional ionospheric Total Electron Content (TEC), This paper provides a detailed introduction to the spherical harmonic function model under the single-layer ionospheric sphericalshell assumption, and using data from 5 monitoring stations in the Xi’an region, regional ionospheric modeling was performed using 3th-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 0.79m (1σ), with horizontal and vertical positioning accuracies of 1.76m and 2.41m, respectively. Compared to using the Global Ionosphere Map (GIM) model, this represents improvements of 56.83%、56.86% and 62.40%, respectively. The ionospheric delay correction effectiveness was markedly improved.