We review the purpose, significance and method of the determination of the Martian space environment's magnetic field by Yinghuo-1(YH-1), the first Chinese Martian space environment exploration orbiter. Most of the scientific objectives of the YH-1 orbiter are related to the Martian space magnetic field, so the magnetometer is considered to be one of the most important payloads. This instrument is designed to work in the harsh environment of the Mars orbit and to collect accurate data of its magnetic field over a long period. The YH-1 magnetometer has a ±256nT dynamic range at 0.01nT resolution, throughout an operation temperature of -140℃ to 75℃. With a total noise level below 0.03nT, the magnetometer can measure three-component magnetic fields from DC to 10Hz. It will operate together with an onboard Plasma Package program to analyze the magnetic field and dynamics of the Martian space environment.