Directionally solidified oxide eutectic ceramic (DSOEC) has been one of the focuses of ceramic materials because of its excellent mechanical properties and oxidation resistance at ultra-high temperature (above 1600 ℃). Al2O3/GdAlO3/ZrO2 ternary DSOEC was prepared with induction heating zone melting method, of which microstructure and mechanical properties’ involution with the growth rate was revealed. As the growth rate increased, the microstructure of Al2O3/GdAlO3/ZrO2 DSOEC became into a complex regular structure from an irregular network structure, and the eutectic spacing decreased continuously. Its fracture toughness increased first from 4.75 to 6.55 MPa m1/2 and then decreased to 5.48 MPa m1/2, while its hardness increased continuously from 12.20 to 15.56 GPa. The third component ZrO2 made GdAlO3 phase microstructure in the binary eutectic Al2O3/GdAlO3 from a complex regular structure transformed into an irregular network one in the ternary Al2O3/GdAlO3/ZrO2 for the low growth rate, while from the regular layered microstructure to the regular triangular one in the ternary eutectic for the high growth rate, ZrO2 phase also increased the eutectic spacing, improved the fracture toughness. The fracture toughness at room temperature (4.75–6.55 MPa m1/2) of Al2O3/GdAlO3/ZrO2 ternary DSOEC was much higher than that of Al2O3/GdAlO3 binary DSOEC (1.47–3.24 MPa m1/2).