Here, the simulation of the physical fields in an n‐type ferroelectric thin‐film transistor (FeTFT) with a bottom contact bottom‐gate configuration is demonstrated. In the off‐state, the intensity of the lateral electric field in the space charge region near the edge of the drain electrode is several times higher than the coercive field of the ferroelectric film, pinning the direction of polarization near the drain electrode along the channel. While the FeTFT switches from off‐state to on‐state, the vertical component of polarization near the drain edge is stronger than other parts near the channel. This enhances the depolarization field in this area so that the retention performance of the on‐state is worse than the off‐state. These results and methods benefit FeTFTs and are also valuable for floating‐gate memory and light‐emitting field‐effect transistors.