A low-loss waveguide structure composed of a silicon-on-insulator （SOI） structure and graphene-coated nanowires （GCNW） is proposed. The dependences of the transmission characteristics of fundamental graphene plasmon mode in the proposed structure on frequency， geometric， material parameters， and chemical potential of graphene are investigated in detail by use of the finite element method. Simulation results show that the low refractive index SiO2 dielectric layer in the waveguide can achieve high-performance deep subwavelength light confinement. Thanks to the high refractive index contrast between the low refractive index SiO2 dielectric layer and the SOI substrate as well as the graphene layer， a low-loss plasmon mode with a very small mode field area is obtained. The proposed waveguide structure provides a certain reference for the design of high-performance and deep sub-wavelength tunable integrated photonic devices.