Abstract: The influence of nano-particles addition on the microstructure and mechanical properties of soldering joint of low silver SAC0307 soldering paste was studied. The results show that the island-like Cu₆Sn₅ phase exists in a larger size and is difficult to keep dispersion in solder eutectic regions with the addition of nano-Cu. When the additive amount of nano-Cu exceeded 0.3%, the Cu₆Sn₅ phase was easy to accumulate, merge and grow up in the liquid/gas interface. This behavior leaded the deterioration of the flowability of solder, and produced large amount of pores because the flux gas in the solder paste is difficult to escape during the soldering process. While there is no pores in solder joints with 0.1%~5.0% nano-Ag addition. The Ag₃Sn phase exists in a tiny size and diffuses distribution in these solder eutectic regions, and the β-Sn primary crystals are refined significantly in solder joints. With the increase of nano-Ag addition, the shear strength increases firstly and then decreases. when the addition is 0.5% the shear strength is the largest, meaning the shear strength in this addition is 30.8% higher than the shear strength of solder joint the SAC0307 solder paste under the same conditions.