Owing to an additional thinner planar waveguide with micron scale is attracted to the symmetrical metal cladding waveguide (SMCW) with sub-millimeter scale, the interference interaction between different Q-value guided modes would generate a Fano reflectivity curve. In our double metal-dielectricmetal waveguides (DMDMW) structure, a Kerr nonlinear medium is located in the guiding layer of the SMCW where the excited oscillating wave is enormously enhanced. Numerical calculations show that a minute variation of the incident light intensity will give rise to a change in the dielectric constant of the Kerr nonlinear medium and lead to positive feedback. A bistable reflection can be achieved with a low threshold and a large modulation depth because of the sharpness and the asymmetricity of the Fano reflectivity curve.