The main causes of the temperature measurement error of Raman distributed optical fiber temperature sensor was researched and discussed based upon the Raman scatting principle and temperature demodulation algorithm. A method to address the effects caused by the attenuation differences between Stokes and anti-Stokes light, additional attenaution of fiber bending, stress and environment changes was proposed. Furthermore, the measurement error caused by dark current produced by the detector was also reduced by using nonlinear equations with three different temperature signals acquired along the same-fiber section location. The experimental results demonstrate that the aritmatic mean error of calibrated system has reduced from 8.0℃ to 0.37℃ with the fiber location found at 900 m. Overall, a temperature arithmatic mean error better than 0.6℃ is achieved.