Abstract: The present disclosure provides a graphene sensor and a preparation method and use thereof, and relates to the technical field of sensors. The graphene sensor according to the present disclosure includes a substrate, and an electrode layer and a functionalized graphene film that are laminated on a single side of the substrate, where the functionalized graphene film is obtained by modifying a graphene film with triethylamine. According to the present disclosure, the triethylamine is used as a probe to modify the graphene film, so that nitrate nitrogen can be sensitively and accurately measured. The graphene sensor according to the present disclosure identifies an object to be measured based on chemical functional groups instead of a biological method, and has low costs and high chemical stability.