In order to obtain a more accurate calculation method for the prestress frictional loss of the duct, and to ensure the effective prestress of the bridge structure design and the safe operation of the bridge structure, based on the Hertz contact theory and the coupling effect between friction force, contact pressure, and tensile force were considered, the formula was derived for the frictional loss of the pure bending duct under non-uniform pressure. The influence of different parameters on the calculated value of the frictional loss was analyzed using finite element software. Exploring the specific distribution of the law of pure bending orifice in the non-uniform pressure prestressing resistance loss through the actual engineering resistance test, and through the specification of the formula, derivation of the formula of the theoretical calculated value and the field measured data of the deviation, to verify the reasonableness of the formula. The results show that for bending angles smaller than 120° and friction coefficients within the range of 0.2 ~ 0.4, the calculated values from the derived formula are closer to the actual situation. With the increase of tensile stress and bending angle, the calculated values of the frictional loss obtained from the derived formula are closer to the measured results.