To synthesize large-area graphene single crystals, we specifically designed a low-pressure chemical vapor deposition (LPCVD) reactor with confined reaction space (L 22 mm × W 13 mm × H 50 μm). Within the confined reaction space, a uniform distribution of reactant concentrations, reduced substrate roughness, and the shift of growth kinetics toward a diffusion-limited regime can be achieved, favoring the preparation of large-area, high-quality graphene single crystals. The gas flow field and mass transport pattern of reactants in the LPCVD system simulated with a finite element method support the advantages of using this confined reaction room for graphene growth. Using this spaceconfined reactor together with the optimized synthesis parameters, we obtained monolayer, highly uniform, and defect-free graphene single crystals of up to ∼0.8 mm in diameter with the field-effect mobility of μ EF ∼ 4800 cm 2 V −1 s −1 at room temperature. In addition, structural design of the confined reaction space by adjusting the reactor's dimensions is of facile controllability and scalability, which demonstrates the superiority and preference of this method for industrial applications.