Graphene exhibits extraordinary opto-electronic properties due to its unique dynamic conductivity, bringing great value in optical sensing, surface plasmon modulation and photonic devices. Based on the polarization-sensitive absorption of graphene working at near infrared to ultraviolet wavelengths, we theoretically investigate the refractive index sensing and imaging mechanism under oblique and tight focusing incidences of light respectively. We demonstrate that such graphene-based methods can provide ultrahigh refractive index resolution (∼2.09×10-8 RIU) for label-free sensing, and high transverse spatial resolution (∼200 nm) and large longitudinal detecting length (∼750 nm) for imaging under 532 nm incident wavelength. The proposed methods could potentially guide future researches in graphene optical detection, non-invasive biological sensing and imaging, and other applications.