Embodiment of the present disclosure provide an apparatus and method to monitor a change of a polarization state resulted from an optical link and an optical receiver, in which by obtaining a change matrix of response matrices at two moments, and determining a parameter characterizing a change of a polarization state resulted from an optical link according to feature values of a change matrix in a Stokes space corresponding to the response matrices. The change of the polarization state resulted from the optical link is dynamically monitored in a real-time manner, independent of a polarization state of an input signal of the optical link, and no extra hardware and control may be needed.