This work aims to investigate effects of annealing duration on transformation from amorphous carbon to graphene via nickel catalyst. The magnetic filtered arc deposition technology was used to prepare amorphous carbon (a-C) film on the SiO2/Si substrate. Then, a layer of nickel was deposited on the amorphous carbon film by magnetron sputtering. Then the sample was put in a pipe furnace for vacuum thermal annealing processing. The chemical valence state of a-C was characterized by X-ray photoelectron spectroscopy. The structure and surface morphology change before and after annealing were investigated with a SEM and the quality of the graphene generated was characterized with Raman spectroscopy. The micro structure of the graphene was characterized with a TEM. The annealing duration greatly affected the graphene generated for transformation of a-C. At 900 ℃, high-quality graphene was obtained in a short time of annealing. Similar high-quality graphene was obtained at 700 ℃ and 800 ℃ after the annealing duration was extended. However, the annealing duration cannot be extended infinitely; otherwise the structure of the graphene might be damaged. Proper extension of annealing duration to 60 min at 700 ℃ to 800 ℃ can improve the quality of the graphene generated and reduce ID/IG from 0.63 to 0.53. TEM shows that 32 layers of graphene can be obtained by annealing at 700 ℃ for 60 min. Graphene of high quality can be obtained by short time (1 min-10 min) of annealing at 900 ℃.