With dark capacitance transient method, electron emission and capture transient processes at deep level, which is located within an energy range of KT above EF in depteled region of zero-biased junction, have been observed in Pt diffused deep diffsion junction of n-Si and p-Si with different background doping density. These transient behaviors agree with the solution of electron variation rate equation of deep level for different initial conditions at that place.In this paper, a machanism is also proposed to explain the occurrence of emission transient. It is considered that the origin of emission transient is closely related to the structure in the deep diffusion junctions and the capture transient to the capture characteristic of different impurity.