New sintering simulation model is proposed and developed by using the discrete granular elements to make quantitative description of neck growth in sintering. The Kuczynski bi-spherical neck growth model is extended into the time-evolution equations in the multi-granular system even with consideration of the particle size distribution. Through comparison with the experimental results for pure copper granulars, the validity and effectiveness of our developed model is verified. Furthermore, the present method can be easily coupled with the powder compaction analysis to describe difference of sinterability with change of initial structure of powder and to simulate the whole mechanical process from powder compaction to sintering.