This paper investigated the influence of sintering temperature on the dielectric performance of alumina ceramic. Three different kinds of alumina ceramic samples were prepared using the same formula with three different sintering temperatures. The flashover voltage and surface charge distribution of the test samples were measured with a finger type electrode system under a positive pulse voltage application in a 1×10-4Pa vacuum circumstance. The experimental results showed that the samples with higher sintering temperature have worse dielectric performance. Based on the SEM observation, the change of dielectric performance could be attributed to the change of microstructure of alumina ceramics.