Abstract: Due to the electrocaloric shock caused by strong transient electric current, the inner resistance sheets in the brake resistors of Shanghai metro cars often deform seriously under the effect of thermomechanical coupling. In the experiment, in order to avoid the temperature field and displacement field being disturbed by contact sensor, non-contact detections are adopted. A far-infrared remote thermometer is used to measure the temperature and a three-dimensional imaging technology based on the digital grating projection and Gray-code is used to measure the thermal deformation. The thermal deformation detection of brake resistors was carried out at thirteen different temperatures, the accuracy of deformation detection reached 0.1mm after system calibration and error control. The application of optical imaging technology in the thermal deformation detection shows a new way for the experimentation of thermal stress.