Abstract: In order to improve the calculation accuracy of the inertial measurement coordinate data of in-service pipelines and thereby promote the pipeline digitization process with high quality, a calculation model of dead reckoning error of a small-caliber inertial measurement unit was proposed on the basis of the information of the inertial measurement unit and the odometer with reference to the smooth filtering algorithm. Through the filter recursive calculation with the established state equation and the measurement equation, the optimal estimated value of the system error can be obtained, and the data accuracy can be guaranteed by solving the ambiguity of the whole cycle with the smoothing filter algorithm. According to the verification of the pipeline inertial measurement results, the pipeline centerline coordinates calculated by the dead reckoning error calculation model are consistent with those collected by GNSS-RTK, and the error can be controlled at the meter level. As the result shows, the calculation model, which is special for reducing dead reckoning error of the small-caliber inertial measurement unit based on the information of the inertial measurement unit and the odometer in combination with the smooth filtering algorithm, can effectively reduce the influence of the pure inertial navigation error accumulation over time on the accuracy of measurement results, and thus it has good application value.