  We study accretion onto the neutron star in Be/X-ray binaries, using a 3D SPH
code and the data imported from a high resolution simulation by Okazaki et al.\
(2002) for a coplanar system with a short period ($P_{\rm orb}=24.3 \rm d$) and
moderate eccentricity $(\rm{e=0.34})$. We find that a time-dependent accretion
disk is formed around the neutron star in Be/X-ray binaries. The disk shrinks
after the periastron passage of the Be star and restores its radius afterwards.
Our simulations show that the truncated Be disk model for Be/X-ray binaries is
consistent with the observed X-ray behavior.
