Abstract: Martian magnetic field measurement is one of the focuses of international Mars exploration mission. China's first Mars magnetic measurement mission would carry magnetometers on the rover and the orbiter to achieve joint observation of the surface magnetic field and the spatial magnetic field. Dual tri-axial fluxgate magnetometer would be carried on the rover,which adopts Helmholtz compensation coil probe technology and all digital closed-loop feedback circuit technology to realize high precision same-point measurement of space magnetic field. Reliability, safety and space environment adaptability of the instrument are well considered in the design. According to ground calibration, the range of the ROVER fluxgate magnetometer is ±65 000 nT,the noise level is 0.01 nT/√Hz,and the resolution achieves 0.01 nT.