In view of a 500kVA substation of Changchun, according to the problem of platinum resistance temperature sensor Pt100 data acquisition of large error in the process temperature measurement of transformer, through the research on the nonlinear characteristic of platinum resistance, propose a negative resistance compensation method and the piecewise least square fitting method combining from the external to the sensor signal to error correction, after testing, the method can effectively improve the measurement accuracy, reduce errors, and good applicability, the compensated sensor can meet the most demanding occasions.