  We investigate the statistical distribution for ideal Bose gases with
constant particle density in the 3D box of volume $V=L^{3}$. By changing linear
size $L$ and imposing different boundary conditions on the system, we present a
numerical analysis on the characteristic temperature and condensate fraction,
and find that the smaller linear size is efficient to increase the
characteristic temperature and condensate fraction. Moreover, there is a
singularity under the antiperiodic boundary condition.
