A good linearity of measuring curve can improve the resolution of valid measure-area. The optical absorption edge is 850nm under the temperature of 25℃. The emission spectrum of the light source used with the sensor should overlap on both sides of the optical absorption edge. The displacement of this edge induced by temperature changes modifies the fraction of light that falls into the absorption band, meaning that transmitted intensity will change. From several equations, the reflected light intensity is closely connected with the temperature of detected object. As the temperature climbs up, the ultimate output light intensity falls down nonlinearly. After that, we have proposed the feasibility to broaden the range of measurement from 20 ℃～80 ℃, as many references discussed, to 10 ℃～90 ℃. Therein two groups of curve about reflected light intensity induced by temperature through the computation of Matlab, three groups of curve on output intensity according to temperature variations, three groups of curve about detected voltage changes under different incident light intensities are concluded. From above, four valuable conclusions are brought into being.