  Mars Orbiter Magnetometer (MOMAG) is one of seven science payloads onboard
Tianwen-1's orbiter. Unlike most of the satellites, Tianwen-1's orbiter is not
magnetically cleaned, and the boom where placed the magnetometer's sensors is
not long enough. These pose many challenges to the magnetic field data
processing. In this paper, we introduce the in-flight calibration process of
the Tianwen-1/MOMAG. The magnetic interference from the spacecraft, including
spacecraft generated dynamic field and slowly-changing offsets are cleaned in
sequence. Then the calibrated magnetic field data are compared with the data
from the Mars Atmosphere and Volatile EvolutioN (MAVEN). We find that some
physical structures in the solar wind are consistent between the two data sets,
and the distributions of the magnetic field strength in the solar wind are very
similar. These results suggest that the in-flight calibration of the MOMAG is
successful and the MOMAG provides reliable data for scientific research.
