The present disclosure provides a local carbon-supply device and a method for preparing a wafer-level graphene single crystal by local carbon supply. The method includes: providing the local carbon-supply device; preparing a nickel-copper alloy substrate, placing the nickel-copper alloy substrate in the local carbon-supply device; placing the local carbon-supply device provided with the nickel-copper alloy substrate in a chamber of a chemical vapor-phase deposition system, and introducing a gaseous carbon source into the local carbon-supply device to grow the graphene single crystal on the nickel-copper alloy substrate. A graphene prepared by embodiments of the present disclosure has the advantages of good crystallinity of a crystal domain, simple preparation condition, low cost, a wider window of condition parameters required for growth, and good repeatability, which lays a foundation for wide application of the wafer-level graphene single crystal in a graphene apparatus and other fields.