A high precision temperature calculation method of fiberoptic distributed temperature sensing system based on iteration technique is introduced. Compared with the traditional calculation methods, this iterationbased method further corrects the attenuation coefficient difference of the Raman antistokes wavelength and stokes wavelength in optical fiber which is temperaturesensitive, thus increases the precision of temperature measurement. It especially works well with the measurements of normaldistance, complex temperature distribution fields. The iterative formula is established by theoretical analysis, the corresponding fiber parameters are premeasured, by programming on data processing module of the sensing system. The result shows great accordance between calculation and actual temperature distribution within the range from 0 to 90℃ along a whole fiber of 5 km.