Based on viscoplastic Anand’s model, the structural stress of 8×8 InSb array detector with underfill dependent on indium bump sizes is systemically researched by finite element method. Simulation results show that as the diameters of indium bump decrease from 36μm to 20μm in step of 2μm, the maximum stress existing in InSb chip first reduces sharply, then increases flatly, and reaches minimum with indium bump diameter 32μm. The maximum stress in Si readout integrated circuit (ROIC) fluctuates at 320MPa with amplitude less than 50MPa, almost half stress in InSb chip. Yet the maximum stress in the indium bump array is almost unchangeable and keeps at 16.3MPa. When the height of indium bump increases from 9μm to 21μm in step of 6μm, the maximal stress in InSb chip first reduces sharply from 800MPa to 500MPa, then almost retains constant. With indium bump diameter 32μm and height 21μm, the maximum stresses in whole 8×8 InSb array detector reaches minimum 458MPa, besides, the stress distribution at the contacts areas is uniform and concentrated, the stress value is smallest and this structure is promising to avoid device invalidation.