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With the development of deep space exploration, miniaturization has become the trend of satellites, which heightens the reliability demand of satellite electronic systems. Solder plays an important role in integrated circuit, providing electronical and mechanical interconnection of electronic devices. To understand the microstructure and performance evolution of solder joints under cosmic irradiation environment and meet the reliability demand of solder joints used on satellites, the effect of γ-ray irradiation on the mechanical performance and microstructure of eutectic SnPb solder joints were investigated. The results show that after γ-ray irradiation, the generation of micro-voids and micro-cracks in Pb-based solid solution are observed due to the accumulation of irradiation damages. Energetic electrons induced by γ photon through Compton Effect, could knock Pb atom out and form point defect, which is the cause of mico-voids and micro-cracks. After 964 kGy irradiation, the tensile force of eutectic SnPb solder joints decreases by 14.12%. Moreover, the analysis of fracture morphology shows that the fracture kinds of eutectic SnPb solder joints before/after γ-ray irradiation are all plastic fractures, but the ductility of eutectic SnPb solder joints is reduced with unobvious dimples.