Reinforced Ag nanoparticles were incorporated into Sn-0.7Cu matrix composite solder by a mechanical means in order to improve the creep properties of the solder matrix. The creep-rupture life was studied of Sn-0.7Cu solder joints and composite solder joints reinforced with Ag nanoparticles at different temperatures and applied stresses. Stress exponents and creep activation energy were calculated for Ag nanoparticle reinforced Sn-Cu matrix composite solder joints at different temperatures and stress levels. Steady-state creep constitutive equation of the composite solder joint was established. Results show that at different temperatures and stresses, Ag nanoparticles reinforced Sn-Cu composite solder joints have higher creep rupture life and creep activation energy than Sn-0.7Cu solder joints. It indicates the creep resistance of the composite solder joint with 1 vol% Ag reinforcement addition is better than that of Sn-0.7Cu solder joint