Abstract: The control of the graphene nucleation density and the number of graphene layers is important for the synthesis of single crystal graphene. Graphene was prepared by an improved chemical vapor deposition (CVD) method on a Cu foil substrate inside a slit in a graphite rod that was a close fit to the silica tube reactor in an oven under a low pressure of 5.5 Torr. The reactor was first heated to 1 273 K at a heating rate of 278 K/min under a flow of a gas mixture of H₂ and Ar (1:5) and annealed for 35 min. Then, a gas mixture of CH₄ and H₂ (1:15) was introduced into the reactor for graphene deposition for different times. Finally, the reactor was cooled to room temperature at a rate of 323 K/min under a flow of the gas mixture of H₂ and Ar (1:5). Results indicate that a low nucleation density was achieved by this method, resulting in graphene with a low defect density. Single-layer graphene was obtained for a deposition time of 20 min. The longer the deposition time, the larger the size, and the more the number of graphene layers.