Abstract:The automatic fluxgate theodolite is an important instrument for measuring the geomagnetic declination and geomagnetic inclination in the absolute observation of geomagnetism. There are nonorthogonal errors of the horizontal axes and magnetic axes,zero offset error of the fluxgate sensor, motor stopdeviation andverticalaxis tiltdeviation duringthe measurement.In order to improve themeasurementaccuracy ofthe instrument,the multibodysystem theoryis usedto establishthe output valuemodelof thefluxgatesensorin thispaper. Based on the model and the "fourposition measurement method", the multiple parameter error compensation algorithm for magnetic declination and inclination is proposed. The compensation algorithm performs measurement through the sensor pointing to four specific positions perpendicular to the geomagnetic vector, which can eliminate nonorthogonal error and sensor zero offset. The compensation algorithms can effectively correct the motor stop deviation and vertical axis tilt deviation during the measurement process. Simulation experiments on simulation data show that the algorithm can effectively compensate the motor stop error and vertical axis tilt error within ±10′. The actual measurement experiments completed at the geomagnetic station show that the compensation algorithm reduces the measurement error to within 3″ and meets the instrument measurement requirements.