<p>Radially loading rotary extrusion (RLRE) is a new plastic forming process that can achieve the integral plastic forming of large conical parts with inner high ribs (CPIHR). However, the plastic deformation behaviors of rib area in this process have not yet been fully revealed. This work combines the finite element method and experimental method to study the changes in metal deformation behaviors when the thickness of the inner rib changes. The results indicate that the thickness of the inner rib and the thickness of the top die has a significant impact on the equivalent strain and metal flow behavior. When the thickness of the inner rib is too small compared to the thickness of the top die, it is easy to cause uneven distribution of equivalent strain in the rib and disorder of the metal flow line. When the thickness of the inner rib is too large compared to the thickness of the top die, it is easy to cause insufficient filling of the inner rib. It has been revealed that there are three typical plastic deformation behaviors during the formation of CPIHR using RLRE method, namely under-filled type, full-filled type, and over-filled type. There is a reasonable choice of top die thickness for different inner rib thicknesses to ensure full filling of the inner rib. Established reasonable top die thickness design criteria for obtaining conical parts with specified thickness inner ribs. And successfully prepared the required CPIHR through experiments, verifying the rationality of using this criterion to design top die of RLRE.</p>