Local delamination failure phenomena of indium antimonide infrared focal plane detectors (InSb IRFPAs) in their mass production have become a bottleneck restricting the improvement of their final yield. In order to determine the inducement of local delamination in InSb IRFPAs, the interface between the InSb chip and the underlying underfill with cohesion units was covered, and the specified parameters in cohesion model were optimized, finally the two-dimensional model of local delamination failure analysis of InSb IRFPAs was established. Simulation results are verified by the measured distribution characteristics of local delaminations, that is, (1) Most local delamination appears in the surrounding edges of InSb chip, and occupies a certain width; (2) Once the InSb chip is separated from the underlying underfill in the normal direction, the local delamination will expand gradually toward its both sides of the plane. In order to clarify the inducement of the local delamination, the evolution rule of the local delamination with different mixed-mode ratios is systematically analyzed under the jointed action of both the opening mode and sliding mode. The simulation results are highly consistent with the measured results when the mixed-mode ratio between the opening mode and the sliding mode is set to 4: 6. The local delamination of the InSb IRFPAs are ascribed to the jointed action of both the interfacial normal stress and the in-plane shear stress, is the typical mixed-mode local delamination mode, furthermore, the sliding local delamination mode is dominant.