The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM) mission is a project of the Strategic Priority Research Program of Chinese Academy of Sciences. It is a dedicated gamma-ray all-sky monitor composed of two microsatellites. Each GECAM satellite is equipped with 25 gamma-ray detectors (GRD) and 8 charged particle detectors (CPD), to measure the positional, temporal and spectral properties of high energy transients. They were launched together to an orbit of 600 km height and 29° inclination angle on December 9, 2020.