Thermal cycling was applied to assess the effect of tin-lead solder 63Sn37Pb and lead-free solder 95.5Sn3.8Ag0.7Cu on the reliability of 3D PLUS solder joints. Nonlinear finite element method and viscoplastic Anand model were used to evaluate the stress and strain distribution and dangerous position of solders under the thermal cycling condition. The law of solder joints stress and plastic strain were finally obtained and showed significant cyclical changes. The stress and strain emerged the trend of accumulated enhancement with the process of time, then ultimately stabilized. Comparing two curves of equivalent stress and plastic strain obtained from lead-free and tin-lead solder, it was found that the reliability of 95.5Sn3.8Ag0.7Cu was better than that of 63Sn37Pb.