Abstract: The optimal polarization filtering is investigated, which can be described as optimization with a nonlinear restriction. The nonlinear restriction is removed through an intermediary variable. According to the extremum necessary condition, the optimization is further transformed into problem of rooting a unitary quadratic equation. Consequently, the maximal SINR is the bigger root of the unitary quadratic equation and the optimal receiving polarization is obtained. The filtering performance is improved with the difference increasing in polarization domains between the desired signal and interference. The completely polarized interference can be suppressed easily and the partially polarized interference is difficult. to be suppressed.