In order to solve the problems of deformation failure and low sensitivity of flexible thin-film thermocouples, a thermoelectric sensing model was established and thermal-electrical-force multi-field coupling simulations of flexible thin-film thermocouples were performed. Based on the results, the structural dimensions of the sensor were optimized, and a process method for optimizing the sensitivity by heat treatment was proposed, so as to prepare a thermoelectric Indium Tin Oxide-Platinum (ITO-Pt) thin-film temperature sensor based on polyimide substrate with high reliability and high sensitivity. The calibration test experiment proves that the sensor sensitivity reaches 40.10 μV / ℃, which can effectively meet the temperature testing requirements of human wearable devices and lithium battery health monitoring.