A deformation reconstruction correction method based on ultra-weak fiber Bragg grating (uwFBG) is proposed to address the issue of local curvature discontinuities in multi-segmented cylindrical pipes. The relationship between the eccentricity of the sensing fiber and its sensitivity in the reconstruction algorithm is analyzed. A multi-point fitting weighted average method is then used to correct the curvature discontinuity points. Simulation results show that the accuracy of the corrected reconstruction algorithm is improved by 4.55% compared to the traditional algorithm. Three uwFBGs are bonded at 120° angles to the outer surface of a 12-meter-long, 75mm outer diameter polypropylene pipe to form a self-packaged deformation sensing unit. Deformation monitoring experiments are conducted, and the results demonstrate that the corrected deformation reconstruction algorithm achieves a normalized error of less than 2.2% at the tail end of the 12-meter pipe, which is an improvement of 1.958% over the original algorithm. This method provides a valuable reference for deep deformation monitoring of hundred-meter-scale engineering structures.