The sintering kinetics model of initial stage by spark plasma sintering (SPS) is discussed in this paper. During SPS, there are discharges among the powder particles. And the particles surface will be melted and form viscose flow. These phenomena accelerate the particles rearrangement and reduce the sintering time. The relationship between the shrinkage ratio of particles and the sintering time during the initial stages of sintering by SPS has been obtained. The results show that L/L0 is linear to the time.