Two-step method is used to research stress and its distribution in 64×64 InSb infrared focal plane array (IRFPA) employing finite element method. First, a small 8×8 InSb IRFPA is systemically studied by varying indium bump diameters, standoff heights and InSb chip thicknesses in suitable range, with indium diameter 30μm, thickness 9μm and InSb thickness 12μm, von Mises stress in InSb chip is the smallest and its distribution is uniform at contacting areas. Then, the sizes of InSb IRFPA is doubled once again from 8×8 to 64×64 to learn the effect from chip sizes, thus, the stress and its distribution of 64×64 InSb IRFPA is obtained in a short time. Simulation results show that von Mises stress maximum in InSb chip almost increases linearly with array scale, yet von Mises stress maximum in Si ROIC decreases slightly with increased array sizes, and the largest von Mises stress is located in InSb chips. Besides, stress distribution on the bottom surface of InSb chip is radiating, and decreases from core to four corners, and stress value at contacting area is smaller than those on its surrounding areas, contrary to stress distribution on top surface of InSb chip.