The invention discloses a pure-oxygen-atmosphere annealing device and method. According to the method, a material required for being annealed is loaded into quartz tubes, the quartz tubes are placed in an aluminum-oxide ceramic sleeve which is uniformly wound by nickel-chromium wires, oxygen of stable flow is introduced into the quartz tubes, the internal furnace temperature is uniformly and slowly increased, heat of a heater is transferred to crystals to be annealed in a radiation manner, and a temperature control instrument controls a heating-up rate, the degree of a constant temperature, the time for constant temperature and a cooling rate, so that the fully-automatic unattended annealing is realized, and the annealing temperature can reach 1,300 DEG C. The pure-oxygen-atmosphere annealing device and method disclosed by the invention are applicable to the pure-oxygen-atmosphere annealing of materials, such as laser crystals, scintillation crystals and the like, the annealing efficiency is high, and the light emitting efficiency of the laser and scintillation crystals can be increased by 20-40%; after annealing, the brightness, transparency, crystalline perfection and optical uniformity of the crystals can be greatly improved; and the pure-oxygen-atmosphere annealing device has the advantages of stable temperature field, simplicity and reliability, good universality and low energy consumption, so that the annealing cost is reduced.