Research shows radial ribs can reduce the axial force acting on the centrifugal compressor but do not involve its impact on the flow of the rotational-stationary disk cavity. By establishing a coupling model of the centrifugal compressor and the ribbed rotational-stationary disk cavity, the flow characteristics of the ribbed rotational-stationary disk cavity and the effect of the complex flow in the cavity on the axial force were studied. The ribbed rotational-stationary disk cavity is in line with the basic flow structure and characteristics of the Batchelor flow pattern, as demonstrated by the results. The radial balance equation derived based on this flow pattern is suitable for describing the radial motion of the fluid in the ribbed cavity; the rib can increase the tangential velocity in the rotating core center and elevate the proportion of core center in the cavity while weakening the effect of the boundary layer in the region close the rotational disk, which increases the swirl ratio in the cavity; based on the radial balance equation, the mechanism of radial ribs on reducing the axial force was proposed from the perspective of complex flow. The mechanism is as follows: By increasing the swirl ratio, the ribs cause the radial pressure gradient in the cavity to increase, and the average pressure acting on the rotational disk surface is reduced, which leads to a reduction in axial force.