When infrared focal plane array detector (IRFPA) is loaded by thermal shock, the temperature non-uniform in the cooling process leads to temperature gradient distribution inside the device. With the couple-field function of ANSYS, the stresses inside IRFPA influenced by temperature gradient are studied. According to the thermal analysis results the time-temperature curve is obtained. Based on the thermal analysis results, the thermal-stress coupling analysis is carried out, and the stress distribution in IRFPA is obtained. From temperature and time, the varied trends of Von Mises stress maximum in InSb chip of thermal conductive mode are compared with that of the model assuming uniform temperature distribution over the entire structure. The results show when there is the temperature gradient in IRFPA, the Von Mises stresses increase rapidly at first then slowly, which is obviously different from the Von Mises stresses changes in the model assuming uniform temperature distribution over the entire structure. The stress increase occures within a beginning time of 0~0.5s, the sharp stress increase in such a short period will severely affect the reliability of the detector. Furthermore, the reasons of InSb chip possible failure are analyzed. That will be helpful to forecast the potential fracture site in InSb chip.