Al2O3-ZrO2 microspheres were prepared by internal gelation method. The effects of Al3+ on the stability of solution and performance of gel spheres were studied. Al3+ had a great influence on the stability of the solutions, and the more of the amount of Al3+, the shorter of the stabilization time. Because Al3+ did not copolymerize with Zr4+ during the sol-gel transformation, the strength of gel sphere added with Al3+ was low and deformed easily as it was squeezed. The results of our experiments well verify Glasser team's speculation and conclusions. At the same time, based on the experimental results, we prepared Al2O3-ZrO2 composite microspheres with higher content of Al2O3 by controlling the pH of the solution. The change curve of viscosity with time and the stabilization time of the solution with different Al3+ dosage were given, which could provide references for industrial mass production. Samples without hydrothermal treatment cracked severely, while the samples hydrothermally treated kept structural integrity with no cracks after calcined. Al2O3-ZrO2 microspheres with no segregation and phase separation were prepared and alumina evenly distributed in the zirconia matrix. When the content of Al2O3 was low, the tetragonal phase was stable. And the cubic phase was obtained when the content of Al2O3 was more.