The invention relates to a humidity sensor based on nano material film. The humidity sensor comprises a flexible polymer substrate, a comb-like interdigital electrode, a graphene based humidity sensitive film, a humidity sensitive film resistor pickup circuit board, a circuit signal line and an air hole casing. The graphene based humidity sensitive film is a multilayer network film composed of a static induced self-assembly polyelectrolyte precursor and a solvent evaporation induced self-assembly graphene film, and prepared on surfaces of the flexible polymer substrate and the comb-like interdigital electrode to form a humidity sensitive film sensing element. The film resistor pickup circuit and the humidity sensitive element are electrically connected together through a contact pin mode; the humidity sensitive element and the signal pickup circuit board are fixed through screws and nuts, and arranged in air hole plastic casing; and the circuit signal line is lead out through a casing lead hole to realize functions of data acquisition, storage, display and alarm. The sensor has the characteristics of stability, reliability, low cost, high sensitivity, good repeatability, and high speed of humidity sensitive response and recovery, etc.