Real-time acquisition and monitoring of temperature data during the operation of harmonic reducers are crucial for timely fault diagnosis and performance optimization. This study presents an in situ integrated film temperature sensor within the harmonic reducer. To minimize the impact of flexspline strain on the accuracy of temperature measurements， finite element analysis was employed to characterize the strain distribution under various operating conditions. Subsequently， the sensor’s structural design was optimized to mitigate strain-induced measurement interference. Utilizing MEMS technology， the film temperature sensor was fabricated， with strain effects compensated to enhance measurement precision. Evaluation results demonstrate a static temperature measurement accuracy of ±0.3%， an accuracy of ±0.047% during wave generator rotation， ±0.23% at 18.39 °C， and ±0.52% at 50.21 °C. Furthermore， repeatability tests conducted between 20 °C and 120 °C yielded standard deviations relative to a reference temperature sensor ranging from 0.072 °C to 0.296 °C， confirming reliable real-time temperature acquisition. These findings indicate that the developed film temperature sensor can accurately monitor the operating temperature of harmonic reducers， providing a valuable tool for improved diagnostic and optimization processes.