Disclosed are a light polarization state detection apparatus, a detection method and a light polarization state modulation method. The light polarization state detection apparatus comprises a lens with a variable birefringence feature as an optical phase modulator, a polarizer as a SOP analyzer, a plurality of common lenses and a CCD as imaging devices, and a data processing and displaying unit. The SOP detection apparatus uses wide special birefringence distribution of birefringence optical elements such as a GRIN lens to obtain the Stokes parameters of light to be measured by CCD single frame imaging, and can rapidly accurately measure the SOP. The SOP detection apparatus is simple in structure, lower in cost without containing any motion parts and electrical modulation devices, and is a fully static full Stokes parameters SOP detection apparatus.