  The significant splitting of $\Lambda$ and $\bar{\Lambda}$ polarization
measured in STAR's Au+Au 7.7GeV collisions seems to be huge and unable to be
described satisfactorily by any single mechanism, thus we revisit and combine
there different mechanisms together on the basis of our PICR hydrodynamic
model, to explain the experimental data. The three mechanisms, i.e. the meson
field mechanism, the freeze-out space-time mechanism, and the QGP's magnetic
field mechanism, lie on different stage of high energy collisions, and thus are
not contradicted with each other. We find that the meson field mechanism is
dominat, while the QGP's magnetic field mechanism is rather trivial, and
freeze-out time effect is restricted by the small FZ time difference, leading
to a hierarchy of $\Delta P_J \gg \Delta P_t \gg \Delta P_m$. Besides, the
combination of different mechanisms could promote the mean value of
polarization splitting from about 3\%-4\% to 4.5\%, which is more close to the
experimental measured mean value of 5.8\%.
