Abstract: Aiming at the internal detection scene in small-diameter pipelines, this paper proposed a small-diameter oil and gas pipeline centerline mapping technology based on MEMS inertial navigation system. The algorithm of velocity, pose and position solution based on strapdown inertial navigation system was developed as well. According to the error equations of strapdown inertial navigation and wheel odometer, Kalman filter was used to compensate and correct the output information of IMU. Finally the high-precision pipeline centerline position information was obtained by fusing ground magnetic marking information. In this paper, the effectiveness of the algorithm was verified by the actual test data of an internal detection project. The simple inertial navigation scheme and the multi-sensor fusion scheme were also compared. The experimental results indicated that the proposed algorithm can control the detection precision within 1 meter per kilometer, which greatly improved the detection ability of simple inertial navigation measurement to meet the detection accuracy of practical engineering applications.