BiFeO₃-BaTiO₃ (BF-BT) ceramics possess both high Curie temperature and excellent piezoelectric properties, and have a quite wide application prospects in high-temperature piezoelectric sensors and actuators. However, the resistivity of BF-BT ceramics is too low at high-temperature, which can lead to deterioration or even failure of the device's high-temperature performance. Therefore, improving the resistance performance of BF-BT ceramics is the key issue that must be addressed before its application. However, as a type of ferrite, it is difficult to improve resistivity through conventional methods, such as doping modification and optimizing sintering system. In this work, an abnormal increase in resistivity was discovered in BF-BT ceramics, which was confirmed to be related to the second phase Bi₂₅FeO₄₀. Microstructural analysis shows that the second phase has a special layered periodic structure, in which every three rows of atoms constitute a period, and most defects concentrate in one layer of atoms. The pure Bi₂₅FeO₄₀ was successfully synthesized using traditional solid phase method and introduced as an additive into the 0.70BF-0.30BT component, which can increase the resistivity at 300 ℃ from 1.03 MΩ·cm to 4.33 MΩ·cm. In addition, the results of COMSOL simulation confirm that introducing this second phase can increase the resistivity of the 0.67BF-0.33BT component by one order of magnitude. According to the energy filtering effect, this special structure with high energy barriers can prevent carrier migration and improve the resistivity of BF-BT ceramics. This work provides a practical and feasible method for improving the resistivity of BF-BT ceramics.