Dielectrics with high permittivity and temperature stability are important for the development of high-temperature multilayer ceramic capacitors (MLCCs). In this study, Ca1?xNa_xTi1?xNb_xSiO₅ (abbreviated as CTS?xNN) ceramics were prepared by solid-phase reaction method. The introduction of NN weakens the long-range ordered displacement of Ti, leading to a significant increase in the dielectric temperature stability. The CTS?2%NN samples exhibit high permittivity (53) and TCC ≤±170 ppm/^°C in the range of ?55°C to 300^°C. The CTS-based ceramics behave high dielectric temperature stability. In addition, the bandgap of the CTS-based ceramics increased significantly, which is favorable for improving the breakdown strength of the material. For x=4% samples, the breakdown strength reaches 621kV/cm. Thus, the designed CTS-based dielectrics are promising for high-temperature capacitors.