Abstract: Provided are a flexible molecularly imprinted sensor for in-situ and in-vivo detection of gamma-aminobutyric acid content in plants, and a preparation method and a detection method thereof. The flexible molecularly imprinted sensor includes: a flexible substrate and a graphene electrode unit, the graphene electrode unit being arranged on the flexible substrate, where the graphene electrode unit includes a conductive track, a working electrode, a counter electrode, and a reference electrode, where the counter electrode and the reference electrode are respectively located on two sides of the working electrode, and the working electrode is successively provided from inside to outside with a first modification layer, a second modification layer, and a third modification layer, the first modification layer including an AuNPs material, the second modification layer including an Fc-Ni3(HITP)2-ZnFe-LDH material, and the third modification layer including a molecularly imprinted polymer (MIP) material.