A large-angle polarization-independent broadband guided-mode-resonant filter is proposed based on two-dimensional honey-comb silicon photonic crystal slab with ultralow refractive-index substrate material like polymethy lmethacry late (PMMA). The broadband operating range is determined firstly based on the dispersion relationship and rigorous coupled wave analysis (RCWA). Then the impact of silicon membrane thickness and air hole size on the performance of proposed device under surface normal incidence is investigated and an optimal set of physical parameters for 1.55 μm communication window is obtained correspondingly. Its performance affected by oblique incidence and polarization is also analyzed. It shows that broad bandwidth over 110 nm can be obtained with greater than 98% normalized transmittance under surface normal incidence. The common bandwidth of two polarizations will reduce with the increase of incident angle. But it can still cover the whole C-band window (from 1525 nm to 1560 nm) with over 98% normalized transmittance when the angle reaches 18°.