In response to the technical issue in Raman distributed optical fiber technology, where the traditional meter-level spatial resolution is insufficient and causes a decrease in system measurement accuracy within sub-spatial resolution fiber segments of the sensing fiber, a threshold coefficient fitting technique based on a one-dimensional peak-seeking method is proposed in this study. Significant temperature measurement errors of up to tens of degrees Celsius are caused by the overlap of Raman scattering signals from non-detection regions when the detection fiber length is shorter than the system’s spatial resolution. This severely limits the technology application in scenarios requiring precise temperature monitoring. To address the above bottleneck, a purely algorithmic approach is introduced, which can reconstruct the temperature field without modifying the hardware. The sensing fiber is globally scanned using a one-dimensional peak-finding algorithm to precisely locate sub-spatial resolution detection fiber regions. At the same time, the peak intensity, full width at half maximum (FWHM), and location are extracted from the temperature rise curve within the fiber under test (FUT). Through pre-calibration experiments, a quantitative fitting model is established between peak temperature rise curves and threshold coefficients, revealing a quantitative mapping relationship between FWHM and sensing distance, as well as length of FUT. The results indicate that FWHM exhibits a significant positive linear correlation with sensing distance, and this correlation is independent of temperature variation. This characteristic enables FWHM to serve as a reliable feature parameter for identifying and detecting the actual length of optical fibres. During real-time measurements, the detection fiber length is determined via the mapping model based on extracted FWHM and location. Then the corresponding threshold coefficient fitting model is selected to compensate for the distorted temperature rise peaks, thereby reconstructing the distributed temperature field. The experimental results demonstrate that over a 10 km sensing distance, the application of this technique significantly enhances the temperature measurement accuracy within the 30 cm detection fiber, achieving 1.5 ℃ compared with the baseline accuracy of 34.7 ℃ before compensation. The conclusions indicate that the proposed threshold coefficient fitting technique, through algorithmic innovation, effectively overcomes the technical limitation of reducing temperature measurement accuracy in sub-spatial resolution regions within Raman distributed fibre optics sensing. The constructed FWHM quantitative mapping model provides a critical basis for threshold compensation, ultimately enabling precise temperature monitoring of sub-metre regions in long-distance sensing contexts. This solution features a streamlined structure, low cost, and easy engineering integration. It provides a novel approach for long-term, high-precision temperature monitoring in fields such as power cable fault orientation, oil and gas pipeline micro-leakage early warning, and civil structural health monitoring.