It was observed that the time-dependent sheath which was formed around the planar target biased by negatively voltage pulse with a finite rise time in the plasma source ion implantation. FResults show that the time-dependent sheath consisted of two parts: the ion matrix sheath development during the pulse rise time and the dynamic sheath motion after attaining the full pulse. The ion matrix sheath development which is in proportion to square root of the pulse time and the pulse rise rate over the plasma density but independent of the ion mass. The dynamic sheath propagates with approximately the ion sound speed.