The invention discloses a broadband-adjustable coplanar waveguide attenuator based on graphene nanosheets, which mainly solves the problems of large size, difficult integration, narrow working frequency band, high manufacturing cost and complex bias circuit of adjustable structure of an existing traditional attenuator. The broadband-adjustable coplanar waveguide attenuator comprises an input port(1), an output port (2), a single-layer dielectric substrate (5), a central conductor strip (4) and a metal floor (3), the central conductor strip is positioned in the middle position of the upper surface of the substrate, the metal floor is positioned at the two sides of the upper surface of the substrate, N pairs of graphene nanosheets (6) are arranged between the central conductor strip and themetal floor, and the graphene nanosheets can be equivalent to a resistor to lose energy, and the energy attenuation is adjusted by adjusting the equivalent resistance value. The invention has the advantages of simple structure, wide bandwidth, adjustable frequency and good matching, and can be used for weighting the amplitude of each unit of a phased array antenna, performing impedance matching of a radio frequency circuit and improving the stability of a radio frequency amplifier.