Abstract: To meet the requirements of low temperature packaging and high temperature operation for wide bandgap semiconductors, the traditional reflow soldering is gradually substituted by the metallic nanoparticle sintering interconnection. However, the high sintering densification is one of necessities to achieve the high reliable packaging. To reveal the mechanism of nano-copper particles sintering interconnection, this paper firstly establishes the relationship between the particle size ratio and the stacking porosity through the three-dimensional (3D) non-isodiametric double sphere stacking modeling. Then, the Monte Carlo simulation is performed to investigate the sintering process of nano-copper particles with different size ratios. Finally, a sintering experiment with the mixture of two types of nano-copper particles is used to validate the proposed models and simulations. The results show that, according to three 3D stacking models, the stacking porosity is lowest when the particle size ratio is between 10∶1 and 5∶1. Through the Monte Carlo simulation, the model with a particle size ratio of 5∶1 has the largest sintering shrinkage. The experiment by mixing the 250 nm and 50 nm nano-copper particle shows the highest relative density of sintered samples when the particle mass ratio is 8∶1, which is consistent with the theoretical calculations. Thus, the proposed method in this study can provide theoretical supports to the nano-copper sintering interconnection application and process optimization in the wide bandgap semiconductor packaging.