An optical sensor for temperature measurement with much higher reflected light power based on Fresnel reflection and a collimator is presented. The sensor includes only a light source, three couplers, two photodetectors and two sensing ends. One of the sensing ends is designed with a collimator which is covered by solidified epoxy resin with an oil-paper cover, and another is a fiber end with protective cladding. The measurement principle is based on relative Fresnel reflective intensity. Various ambient temperatures are measured in the experiment. The measured data is fitted to linear equation very well. Experiment is implemented by comparing the performances of the fiber-sensor and the collimator-sensor, and the latter shows a much higher reflected light power which means a high signal to noise ratio (SNR) and longer measurement distance may be gained. This is very important and useful for long distance measurement and the situation of many sensors working in parallel mode, which is sensitive to the reflected light power.