<p>The Low Orbit Pearl Satellite series consists of six constellations, with each constellation consisting of three identical micro-satellites which line up just like a string of pearls. The first constellation of three satellites were launched on September 29, 2017, with an inclination of ~ 35.5° and ~ 600 km altitude. Each satellite is equipped with three identical Fluxgate Magnetometers (FGM), which measure the in-situ magnetic field and its low frequency fluctuations in the Earth’s low altitude orbit. The triple sensor configuration enables separation of stray field effects generated by the spacecraft from the ambient magnetic field [e.g. Zhang et al., 2006]. This paper gives a general description of the magnetometer about the instrument design, calibration before launch, in flight calibration, as well as the in-flight performance and initial results. Unprecedented spatial coverage resolution of the magnetic field measurements allow for investigating the dynamic processes and electric currents of ionosphere and magnetosphere, especially for the ring current and equatorial electrojet (EEJ) during both geomagnetic quiet conditions and storms. It could be important for studying the method to separate their contributions of the M-I current system.</p>