Abstract: System in package (SiP) has become a key breakthrough in the post-Moore era with its heterogeneous integration and three-dimensional interconnection technology. Multi-level interconnection structures are integrated inside it, with structural dimensions spanning three orders of magnitude. However, due to the reduction of its interconnection dimensions, the cost and difficulty of traditional analysis methods increase significantly, necessitating a fast and accurate evaluation method. The morphology of interconnection solder joints was predicted, and based on the prediction results, an equivalent simplified SiP device model and sub-models for controlled collapsed chip connection (C4) and chip connection (C2) were established, reducing the difficulty of simulation calculation. Subsequently, thermal cycling finite element simulation calculation of the SiP device under actual operating conditions was carried out via the sub-model finite element analysis method; critical points of stress were determined, and sub-model calculations were performed at the corresponding locations. The predicted lifetimes of different interconnection structures were compared, and the optimal interconnection structure was finally determined.