In this work the difference of annealing behaviors of VO (A-center) in varied doses of neutron-irradiated Czochralski silicon (S1: (5×1017n/cm2) and S2: (1.07×1019n/cm2)) was studied. The vacancy-oxygen complex (VO) is one of the main defects formed in neutron-irradiated Czochralski silicon (CZ-Si). In this defect, the oxygen atom shares a vacancy, it is bonded to two silicon neighbors. Annealed at 200℃, divacancies are trapped by Oi to form the V2O (840cm-1). With the decrease in the 829cm-1 (VO) three infrared absorption bands at 825, 834 and 840cm-1 (V2O) rise after being annealed at the temperature range of 200-500℃. After being annealed at 450-500℃ the main absorption bands in the S1 sample are 834, 825 and 889cm-1 (VO2), and 825 and 919.6cm-1 (O-V-O) in S2. Annealing of the A-center in varied neutron-irradiated CZ-Si consists of two processes. The first is trapping of VO by interstitial oxygen (Oi) in low-dose neutron-irradiated CZ-Si (S1) and the second is capturing of the wandering vacancy by VO, etc, in high-dose neutron-irradiated CZ-Si (S2). The VO2 and O-V-O defects play an important role in the annealing of the A-center. With the increase in the irradiation dose, the annealing behavior of the A-center is changed and the formation of the VO2 is depressed.