The invention discloses a glass ceramic dielectric with high breakdown strength suitable for usage in high voltage direct current environment and a preparation method thereof, and belongs to the technical field of glass ceramic dielectric. The glass ceramic dielectric comprises a composition of xPbO-yBaO-zSrO-aNb2O5-bNa2O-cSiO2-dR, and x, y, z, a, b, c and d satisfy the relations of: 0<=x<=17.1, 0<=y<=17.5, 0<=z<=14.3, 10.7<=a<=34, 11<=b<=25.4, 28<=c<=47, and 0<=d<=4.5; R represents an auxiliary component, which is at least one selected from MnO2, MgO, CaO and ZnO; and x, y, z, a, b, c and d represent molar ratios. The glass ceramic dielectric provided by the invention has advantages of high breakdown strength, high dielectric constant and good dielectric constant temperature stability, and realizes no pore and direct current breakdown strength higher than 50kV / mm.