The invention discloses toughened ceramic for an insulator and a preparation method of the toughened ceramic. The toughened ceramic is prepared from, by weight, 2-3 parts of aluminum borate whiskers, 70-80 parts of silicon carbide micro powder with the proper size, 20-30 parts of aluminum nitride micro powder with the proper size, 1-1.5 parts of calcium fluoride powder, 10-15 parts of carbon powder, 10-15 parts of molybdenum silicide, 6-8 parts of ethyl orthosilicate, 3-5 parts of absolute ethyl alcohol, 3-5 parts of purified water and 1.5-2.5 parts of thermoplastic phenolic resin. By means of the steps of raw material preparation, insulator pre-preparation, insulator sintering and completing, the high-tenacity insulation ceramic with the volume resistivity larger than or equal to 2*1,013 omega-cm, the dielectric strength larger than or equal to 750 kV/cm, the thermal conductivity larger than or equal to 25 W/m.K, the bending strength larger than or equal to 400 Mpa, the Young modulus larger than or equal to 320 Gpa and the breaking tenacity larger than or equal to 25 Mpa is formed. The toughened ceramic is good in economical efficiency, resistant to high temperature oxidation and high in breaking tenacity, and the functions of main materials complement one another.