Abstract: Nanosilver paste can achieve low-temperature sintering and high-temperature service, due to its special size effect and high specific surface area, which has a broad application prospect in the third-generation semiconductor packaging. However, the sintering mechanism of nanoparticles has not been clear and the thermal conductivity has decreased significantly after sintering, which needs to be further investigated. In this paper, the sintering process of silver nanoparticles was simulated by molecular dynamics simulation. The correctness of the potential function was verified by the calculation of thermal conductivity, firstly. And then the microstructural changes of silver nanoparticles were observed, the relationship between the sintering neck growth length and the sintering time was obtained, and the change of the phonon thermal conductivity at the sintering neck was also calculated. Finally, the experimental silver nanoparticles with the same characteristics as the simulation results were observed by the transmission electron microscope. The results showed that the fivefold twins were the stable structure of nanoparticles after sintering, the sintering neck length growth during nanoparticle sintering was a power function of time, and the microstructure at the sintering neck reduced the thermal conductivity of nanosilver by 4.42%.