The reliability of the flip chip package under vibration was investigated. The stress values of the package under forced vibration were calculated using ANSYS code. The vibration induced fatigue life of the flip chip package was found based on the stress-cycle curve of the solder bump. The vibration experiment was performed for the flip chip package to validate the numerical results. The relations between the external force and the acceleration of the package without added mass were established first; then they were applied in the analysis to evaluate the fatigue life of the flip chip package under harmonic vibration. The results show that a longer fatigue life or a better reliability of the flip chip package was obtained for thicker die in the package, for larger fillet angles and larger Young's modulus of the underfill, and for the package under higher external excitation frequencies.