Abstract: To enhance the tunability of subwavelength grating/waveguide structure for Fano resonance, the embedded graphene monolayer was replaced by graphene-dielectric stack as a buffer layer. The improved structure was simulated by using the method of rigorous coupled-wave analysis. Nanoscale dielectric thickness in each stack cell can strengthen the effects of the alteration of graphene's conductivity on the equivalent permittivity of stack structure. The results show that, if the system is exploited as an efficient photoswitch, the demanded change of chemical potential of grapheme decreases from original 0.06eV down to 0.02eV and the modulation depth of the switch is up to 94%. If the system is employed as a tunable absorber, the frequency modulation depth of absorption spectrum is raised from 0.14THz to 0.36THz and the tuning range is extended greatly. The improved structure strengthens the tunability of system for Fano resonance.