The invention discloses an alkaline graphene-nickel electroplating liquid, and a preparation method and an application thereof. The electroplating liquid comprises a nickel salt, a complexing agent, water as a solvent, a reducing agent, a stabilizer, graphene and the like; the graphene is uniformly dispersed in the electroplating liquid, and the electroplating liquid is alkaline. A method for preparing a graphene-nickel composite plating layer by using the electroplating liquid comprises the steps that a to-be-electroplated workpiece as a cathode and a pure nickel piece as an anode are placed in the electroplating liquid and subjected to electroplating operation, and thus the plating layer is formed on a metal surface of the workpiece. In the electroplating liquid, any surfactant does not require to be added, and graphene can be uniformly dispersed and stably exist; with use of the electroplating liquid, the graphene-nickel composite plating layer is formed by means of a simple electrodeposition process, no complex equipment is required, the process is simple and controllable, the cost is low, the electroplating liquid is suitable for production with large area, the obtained plating layer is smooth and compact, the graphene is uniformly distributed, and the obtained plating layer has excellent comprehensive properties and has a better protection effect to a substrate.