Abstract: The Mars Orbiter MAGnetometer (MOMAG) is a scientific instrument onboard the orbiter of China’s first mission for Mars — Tianwen-1. Since November 13, 2021, it has been recording magnetic field data from the solar wind to the magnetic pile-up region surrounding Mars. Here we present its in-flight performance and first science results, based on its first one and one-half months’ data. Comparing these early MOMAG observations to the magnetic field data in the solar wind from NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we report that the MOMAG magnetic field data are at the same level in magnitude, and describe the same magnetic structures with similar variations in three components. We recognize 158 clear bow shock (BS) crossings in these MOMAG data; their locations match well statistically with the modeled average BS. We also identify and compare five pairs of datasets collected when Tianwen-1’s orbiter and the MAVEN probe made simultaneous BS crossings. These BS crossings confirm the global shape of modeled BS, as well as the south-north asymmetry of the Martian BS. Two cases presented in this paper suggest that the BS is probably more dynamic at flank than near the nose. So far, MOMAG performs well, and provides accurate magnetic field vectors. MOMAG is continuously scanning the magnetic field surrounding Mars. Data from MOMAG’s measurements complement data from MAVEN and will undoubt edly advance our understanding of the plasma environment of Mars.