Abstract: [Objectives] The panel and web of laser welded metal I sandwich plate are connected by laser welding. Due to welding defects, the stress concentration of the joint is large so that it is necessary to study the interface fatigue debonding characteristics of metal sandwich plate. [Methods]Based on the cohesive force model theory, considering the time history, the damage evolution equation of 3D structural nodes with multiple degrees of freedom and the convergence criterion, the interface fatigue debonding simulation program suitable for 3D complex structures was developed. The accuracy of the developed program was verified by comparing with the experimental results of welding joint debonding, and the interface fatigue debonding behavior of steel metal I sandwich plate was simulated numerically. [Results]The maximum simulation error of the 3D interface fatigue debonding test was only 14.05%. When the I-type sandwich plate is subjected to the out-of-plane load, the debonding failure at the interface of the sandwich plate is mainly manifested as the surface crack propagation in the direction of the extended weld. When the crack propagation reaches about 70% of the length of the sandwich plate, the crack begins to penetrate through the web to form a penetrating crack. [Conclusions] The developed interface fatigue debonding program can effectively evaluate the interface fatigue debonding life of metal sandwich plates, and has certain guiding significance for practical engineering applications.