When the ratio of Ba/Na was 2, the optimization of dielectric breakdown performance and dielectric constant was obtained. The as-devitrified (4BaO, Na2O)–Nb2O5–SiO2 glass–ceramic exhibits a large dielectric breakdown strength of 864 kV/cm with a stable dielectric constant of about 150 over the temperature range of −50 °C to 100 °C.