Based on the simulated aerospace thermal cycling tests, the effect of thermal cycle on the void damage evolution mechanism of LF6 aluminum alloy welded joint was investigated. The results show that micro-voids form around the second phase particles under the thermal cycling tests. The thermal stress coupled with external stress leads to dislocations pile-up around the particles, and when the dislocation density reaches a certain degree, the stress concentration will exceed the bonding strength at the interface between particles and matrix, resulting in the formation of micro-cracks. The numerical simulation is successfully implemented with the finite element to describe the void damage evolution of the welded joint under thermal cycling conditions.