Abstract: This paper presents a method of calibrating the onboard magnetometer. Firstly, the three-component magnetic sensor of the high-precision ground magnetometer device is placed in the magnetic field ring formed by the standard magnetic field source generator, and the first group of the magnetic field data are collected by the back-end data processing device, and the solenoid coil constant C_i in different ranges is calibrated. Then, the satellite-borne magnetometer is placed inside the magnetic field ring formed by the above standard magnetic field source generator, and the coil constant C_i obtained in different ranges of the high-precision ground magnetometer is taken as the reference to obtain the second group of magnetic field data through the back-end data processing device. Finally, the above two groups of magnetic field data are compared to obtain the calibration values of the range, the resolution, and the stability of the satellite-borne magnetometer. The uncertainty of the calibration results for all parameters of the above calibration items is u=0.12% (k=2). The method has been successfully applied to the calibration of magnetometers for a variety of military and civilian satellites.