The Sn-Ag3.0-Cu0.5/Cu solder joint samples subjected to 2 reflows and different aging time were prepared using, SMT full-automatic reflow machine and high constant-temperature test chamber, the thicknesses of the intermetallic compounds (IMC) of the samples were measured. The results show that the thickness increment of IMC is approximately proportional to the square root of aging time. A series of thermal cycling simulations were conducted with finite element software ANSYS to examine the stress/strain behaviors of PBGA solder joints with various IMC thickness, and the solder balls were characterized by Anand unified viscoplastic constitutive model. The simulated results show that there is the most cumulative plastic strain at the top right corner of the solder ball right beneath the edge of chip, which is considered as the critical solder joint of PBGA. With increasing thickness of IMC, the equivalent stress level of the critical solder joint decreases during the thermal cycling process, the shear plastic strain range Δγ increases and the corresponding thermal fatigue life Nf decreases. The shear plastic strain increment during the heating process and holding process constitutes Δγ and the percentage of Δγ basically maintains at the level of 95% in different IMC thicknesses.