Abstract: Constrained by component performance and inherent resistance-temperature nonlinearity, the operational temperature range of NTC thermistor thermometers is currently limited primarily to-50 ℃ to 150 ℃. They are widely deployed in applications with modest temperature accuracy requirements, such as home appliances, consumer electronics, and automotive systems. To overcome the limitations of low upper-temperature tolerance and inadequate wide-range accuracy in conventional NTC thermistors, this research focuses on developing calibration methodologies for high-temperature NTC thermistors with an extended upper operating limit of 300 ℃.Multiple variants of high-temperature NTC thermistors, featuring different combinations of B-constant values and R₂₅ values（resistance at 25 ℃）, underwent thermal stabilization processes. These included annealing and high-to-low temperature cyclic stress testing. Specimens meeting predetermined stability metrics were selected through this screening protocol. Selected units were calibrated via the comparison method in precision thermostatic baths across multiple discrete temperature points. Continuous polynomial fits of the 1/T versus ln R relationship were computed at various polynomial orders. Resulting coefficients were applied to calculate fitting residuals at multiple independent validation points（non-fitting points）. The optimal polynomial order was determined through systematic evaluation of residuals across different fitting orders. Using this validated optimal polynomial order, calibration coefficients were derived from varying numbers of calibration point combinations. Residuals at validation points were recalculated. A comprehensive residual analysis across different calibration point quantities established the optimal number of calibration points.