Dielectrics with high permittivity and temperature stability are important for the development of high-temperature multilayer ceramic capacitors (MLCCs). In this study, Ca${}_{1?x}$Na_xTi${}_{1?x}$Nb_xSiO₅ (abbreviated as CTS$?x$NN) 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 $\le \pm 170$ 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 621$$kV/cm. Thus, the designed CTS-based dielectrics are promising for high-temperature capacitors.