The magnetic sensitivity of fiber-optic gyroscope (FOG) in radial magnetic field, which is parallel to optical fiber coil plane, is studied. The optical fiber twist, which is the main mechanism of the radial magnetic sensitivity, is analysed. Based on this mechanism, the use of compensation fiber ring to inhibit FOG radial magnetic sensitivity is proposed. By controlling the twist characteristics of the compensation optical fiber, a controllable phase is introduced to offset the radial magnetic sensitivity error of the original optical fiber ring. The model of the relationship between the compensation phase, radial magnetic sensitivity axis associated and the twist characteristics of optical fiber is established. The data simulation and experiment are carried out. By defining the compensation efficiency, inhibition effect of the radial magnetic sensitivity is evaluated. In experimental results, radial magnetic sensitivity compensation efficiency is 63.76%, and the synthesized magnetic sensitivity compensation efficiency is 42.83%. To a certain extent, this method can inhibit the radial magnetic sensitivity of FOG.