We grew Cr4+:YAG crystal with high optical quality by Czochralski method using divalent Ca ions as charge compensation ions. Furthermore, we also annealed the as-grown crystal in air at 1450℃ for 50 hours. Absorption spectra show that the content of Cr4+ ions and absorption coefficient at 1.06μm in Cr4+:YAG crystal annealed increase remarkably. In addition, we also researched Q-switching experiments of lamp pump Nd:YAG laser using Cr4+:YAG crystal with different thickness as absorbers. The results indicate that grown Cr4+:YAG crystal can Q-switch effectively Nd:YAG laser.