The internal structure of the Earth and its geomagnetic distribution and spatial environment can be studied by exploring the near-Earth magnetic field. The China Seismo-Electromagnetic Satellite (CSES) is the first satellite of this kind in a near-Earth orbit. Its scientific goals include the real-time monitoring of electromagnetic changes by studying the Earth system

especially the ionosphere and the mutual actions of other spheres. Obtaining information on ionospheric response before and after an earthquake is the main goal. The magnetic field is one of the most important physical parameters for monitoring the ionosphere. A High-Precision Magnetometer (HPM) is responsible for the accurate measurement of magnetic field vector components from DC to 15 Hz.The magnetic environment of the spacecraft and the vector value accuracy requirement for magnetic field detection are considered. The HPM consists of two fluxgate sensors and a CDSM scalar sensor. The fluxgate sensors provide the vector components of the magnetic field but with limited accuracy and long-term stability. The CDSM sensor measures the scalar of the magnetic field with high accuracy and stability and is therefore used to calibrate the vector data. Satellite remanence magnetic interferences can be reduced with the help of two fluxgate sensors.Several ground data processing methods used to obtain the actual accuracy vector magnetic field data were considered

including the physical calibration of the single sensor

the absolute vector correction algorithm

the remanence magnetic interference elimination

and the coordination conversion method. Several ground calibration tests were conducted to obtain the actual performances.This article also introduces the development of sensors and electronics

as well as provides the data processing procedure and method

and the calibration results.Several algorithms were developed and presented in this article according to the requirement of the ground data processing method. Several key calibration tests were conducted to obtain the linearity

the thermal drift results

the coordination relations between the FGM magnetic axis and the sensor structure

the disturbances of sensors

and the heading error of the CDSM sensor. The results are shown in the table below. Calibration results show that the performances of the HPM satisfy the specifications.HPM development provides a magnetic field exploration method for a near-earth orbit satellite. The schedule indicates that HPM has completed all development and calibration works before the satellite launch. All the performances and data processing procedures satisfy the requirements defined for the CSES mission.