In this paper, the hindering effect of the core-cladding interface (CCI) in thermally poled optical fiber is investigated based on the two-dimensional charge dynamics model. The influence of the mobility of charge carriers at the CCI, and the mobility and concentration of charge carriers in the fiber core on the thermal poling process is presented. It is found that lower mobility of charge carriers at the CCI is responsible for the hindering effect of the CCI. The hindering effect of the CCI could either be enhanced by increasing the mobility and concentration of charge carriers in the fiber core or be overcome by decreasing the mobility and concentration of sodium ions in the fiber core, which could increase the χ(2) in propagation mode. The results provide theoretical insight into the underlying mechanism of the hindering effect and may find applications in thermal poling optical waveguides and multilayered structures.