In the new international system of units, the Kibble balance is one of the most important experimental devices for realization of the mass unit, kilogram. The core element of the Kibble balance experiment device is the magnet system that provides the magnetic field measurement. The magnetic flux density generated at the position of the coil is integrated along the coil wire to form the magnetic geometry factor, and the equivalent relationship between the electromagnetic power and the mechanical power is constructed, and then the measured mass can be determined. Therefore, the performance of the magnetic field generated by the Kibble magnet system significantly affects the final mass measurement accuracy. This paper analyzes how the magnet system affects the Kibble balance uncertainty and reviews the performance of various Kibble balance magnet systems. The comparison of different magnet systems is analyzed and evaluated. It shows that the radial magnet system based on magnetic yoke, represented by BIPM magnet design, has merits in efficiency of magnetic field generation, magnetic shielding and geometrical symmetry, which can be considered as one of the best Kibble balance magnet designs.