Abstract: Based on Anand model, finite element method was used to analyze the stress-strain response of Sn3.8Ag0.7Cu-X(Ce,Fe) solder joints in WLCSP device, and the fatigue life of solder joints were calculated using fatigue life prediction model. The results indicated that deformation of the WLCSP device in service was found, and the significant warp of the PCB can be observed, the deformation-stress-strain in the ball array increased obviously from central solder joint to corner solder joint, the corner solder joints under the chip become the danger area of the whole device. The fatigue lives of SnAgCu, SnAgCuCe and SnAgCuFe solder joints were calculated, it was found that the fatigue life of SnAgCuCe and SnAgCuFe were higher than SnAgCu solder joints, which demonstrated in theory that the addition of Ce and Fe can improve the fatigue life of SnAgCu solder joints, which can provide the theory support for the researches of lead-free solders.