Abstract: To achieve autonomous high-precision well trajectory measurements a well trajectory measurement program based on an improved attitude heading reference system including two gyroscopes and three accelerometers to form inertial measurement unit was proposed. The attitude angles could be gained by the output data from the inertial measurement unit, and then three-dimensional position of the well trajectory could be computed with the known length of the rope used spacial integral. The simulation results show that the algorithm overcomes the shortcomings of the emanative inertial navigation position error over time and has high position accuracy, the scheme reduces the volume of the inclinometer, lower cost and power consumption so that it is suitable for the well trajectory.