A three dimensional geographic coordinate measuring method by using a Pipeline Inspection Gauge(PIG)carried with a Inertial Measurement Unit(IMU)is explored. The method uses a Strapdown Inertial Navigation System (SINS) to position and is accompanied by a Kalman filter estimation algorithm to correct information to solve the SINS divergence calculation problem. The measuring device is mounted in the PIG. The PIG records the inertial signals when the PIG moving in the pipeline. Then, three dimensional geographic coordinates are obtained by off-line calculation, and the attitude incline of the IMU and the speed of the odometer are used to correct the error of the SINS calculation. Finally, a nine dimensional Kalman filter model equation is established, and it is calculated by using the extended Kalman filter algorithm. The experiment for a 30 m pipeline shows that the measurement accuracy is 0.28 m, which indicates that the three dimensional geographic coordinate of the pipeline is able to be measured accurately in in-detecting conditions by the proposed correction algorithm.