In　fiber　optical　parametric　amplifiers　(FOPAs),　the　output　states　of　polarization　(SOPs)　of　both　the　signal　and　the　idler　are　affected　by　the　pump　SOP　through　the　polarization　pulling　effect.　We　proposed　a　normalized　model　to　characterize　the　general　dynamics　of　polarization　pulling　in　degenerated　pump　FOPAs.　By　using　this　model,　we　determined　the　relationship　between　the　output　degree　of　polarization　(DOP)　and　the　gain　of　the　FOPAs　over　three　orders　of　magnitude　changes　in　polarization-mode　dispersion　(PMD)　coefficient.　We　demonstrated　numerically　that　when　fibers　with　typical　PMD　coefficients　are　used,　the　output　signals　of　the　FOPAs　can　achieve　higher　DOP　than　those　of　co-propagating　fiber　Raman　amplifiers,　which　depends　on　whether　the　parametric　gain　is　sufficiently　large　to　compensate　the　PMD-induced　phase　mismatch.　We　also　found　that　for　FOPAs　using　different　types　of　fibers　with　moderate　PMD　coefficients,　this　DOP-gain　relationship　exhibits　highly　similar　behaviors.　We　thus　adopted　a　set　of　modified　empirical　formulas　to　analyze　this　relationship.　This　formula　can　also　describe　the　relationship　between　the　output　DOP　and　the　conversion　efficiency　of　the　idler.　The　results　indicate　that　in　all　cases　studied,　FOPAs　achieve　much　stronger　polarization　pulling　to　the　idlers　than　the　signals.