Al2O3 crystals with different Cr3+ concentrations were prepared by optical floating zone method, and cylindrical Cr∶Al2O3 crystals with different diameters (2 mm to 13 mm) and lengths greater than 100 mm were prepared. The densities of powder rods, ceramic rods and crystals obtained at different stages of Cr∶Al2O3 crystal preparation are measured to be 0.928, 2.230 and 4.051 g/cm3, respectively. XRD patterns show that Cr∶Al2O3 crystal is α-Al2O3 phase. The transmission spectra show that the transmittance of Cr∶Al2O3 crystal in visible light non-characteristic absorption band is more than 80%. The absorption spectra and photoluminescence excitation (PLE) spectra (monitoring 669 nm light) show that there are strong absorption bands at 418 and 559 nm, corresponding to the transitions of Cr3+ from 4A2 to 4T1and from 4A2 to 4T2, respectively. Under the excitation of light with a wavelength of 559 nm, the photoluminescence (PL) spectra of Cr∶Al2O3 crystals show a strong emission peak at 669 nm. At low Cr3+ concentration, the intensities of the peaks increase with Cr3+ concentration increasing, and reach the maximum value in Cr0.006 0Al1.994 0O3 crystal, and then decrease with the increase of Cr3+ concentration.