Flip chip bonding is an advanced microelectronic packaging technology, which has been developed rapidly in recent years. This paper mainly studies the stress of flip chip bonding process, which provides theoretical basis for the research and development of high density flip bonding equipment. The control of bonding force is a key technology of flip chip bonding process, which can directly affect the deformation of bumps. And the quality of bumps will affect the reliability of reflow soldering, filling glue in the bottom surface and other follow-up processes. In addition, the impact and volatility of bonding force will also result in fragmentation of brittle chip, so that the chip will be invalidation and scrapping. Therefore, based on the theory of stress intensity and aimed at the flip chip bonding, we establish the basic model of chip bonding in this paper. We have studied the relationship between bonding force and deformation of bumps and the relationship between bonding force and fragmentation of the chip by the simulation. And the finite element model is verified and modified based on the experiment result. Finally, we obtain an assessment method of the reliability of flip chip bonding, and this method can be used for the research and development of bonding equipment.