  Recently a retrograde neutron star is proposed for the classical wind-fed
X-ray pulsar, GX 301-2, to explain the orbital spin-up to spin-down reversal
near periastron, based on the stream model invoked to explain the
pre-periastron flare of GX 301-2 previously. We study in detail three rare
spin-up events detected by Fermi/GBM and find that the spin derivatives are
correlated with the Swift/BAT fluxes, following a relation of $\dot{\nu}\propto
F^{0.75\pm0.05}$. All the spin-up events of GX 301-2 started about 10 days
after the periastron, which is the time needed for tidally stripped gas to
reach the neutron star. The slow rotation of the optical companion implies that
the accreted matter is likely to have angular momentum in the direction of the
orbital motion, as in a Roche-Lobe-like overflow. As a result, the spin-up
events of GX 301-2 would favor accretion of a prograde disk to a prograde
neutron star. We also find that the flare of intrinsic X-ray emission of GX
301-2 happened 0.4 days before periastron, while the flare of low energy
emission (2-10 keV) happened about 1.4 days before periastron. The preceding
low energy flare can be explained by stronger absorption of the intrinsic X-ray
emission closer to the periastron. This finding weakened the need of the stream
model. The pulse fraction of GX 301-2 near periastron is reduced heavily, which
is likely caused by Compton scattering process. Compton reflection from the
optical companion might be responsible for the observed orbital spin reversal
of GX 301-2.
