  We numerically investigate the dust charging in the sheath, by using the
usual fluid approximation, it is extended to include self consistently the dust
charge variation. The grain charge becomes a new self consistent dynamic
variable, it is found that dust grains are first charged negatively at the
sheath edge and then begin to be charged positively in the sheath. The
numerical results show that the initial velocity of dust charged grains, sized
grains and the density ratio of ion to electron at the sheath edge have
affected the neutral point of dust charge. Moreover, the neutral point of dust
charge affects the spatial distribution of dust density.
