Based on viscoplastic Anand model, von Mises stress distribution of the infrared focal plane array detector is analyzed by finite element method. Simulation results show that as the diameters of the indium bump decreases from 36μm to 18μm in step of 2μm, the maximum stress existing in InSb chip reduces at first, then increases linearly with indium bump diameters. Yet the stress distribution in the indium bump is almost unchangeable and its maximum value keeps at 15.7MPa. Furthermore the maximum stress in Si-CMOS readout integrated circuit is smaller than that of InSb chip, and its changing tendency chart is almost the same as that of InSb chip. When the diameter of the indium bump is set to 30μm, the maximum stresses existing in both InSb chip and Si CMOS readout integrated circuit reach the minimal value 260MPa and 140MPa, respectively. Simulations also show that the stress distribution at the contact areas is uniform and concentrated, the stress value in the whole infrared focal plane array detector is smallest, and its distribution is promising.