Overview: High-precision and high-sensitivity temperature sensors are indispensable tools for material processing and biological cell research. For example, the temperature generated from biochemical reactions is a crucial indicator in the research of drugs in cells. However, the drug produces less heat through biochemical reactions in cells, and the cell volume is limited. Furthermore, the existing temperature sensor can only give a rough temperature range when measuring a very small heat source, so the high-sensitivity and high-precision measurement purpose cannot be achieved. Therefore, it requires a method that can accurately measure small-area heat sources. A static temperature sensor of non-contact cantilever beam is designed to measure the temperature of small-area heat sources and simplify the system design. The temperature sensitive element of the sensor is a silicon nitride cantilever beam which is coated with metal on its upper surface. Due to the difference of thermal expansion coefficients between metal and silicon nitride, the cantilever beam will bend in the direction where the temperature gradient changes rapidly when the ambient temperature of the cantilever beam changes, and the bending amount is measured by optical lever. The relationship between the temperature and the output voltage of the detector can be established by converting the bending amount into electrical signals with the detector. Through the theoretical analysis, the result shows that the bending amount is positively correlated with the change of temperature. Under the laboratory conditions, the relationship between the detector output voltage and the standard temperature can be established as y = 4.8603x - 116.36 by calibration. The goodness of fit is greater than 0.99, the sensitivity is 4.86 mV/℃, and the temperature resolution is 0.04 ℃. To verify the applicability of this method for measuring small-area heat sources, we used the property of the NaYF4 material that can generate heat when excited by laser. We also set up heat sources with different areas and measure the heat generated by the heat source. The results show that it still can be measured even the heating area is only 0.07 mm2. Finally, we prove the correctness of the experimental results by analyzing the relationship between the spectrum of the excited emission of NaYF4 and temperature. Thereby, the purpose of accurately measuring the temperature of the small-area heat source is realized.