Aluminum wheel flow forming is a combined technique of spinning and flow forming, which produces parts with complex axisymmetric geometries and reduces wall thickness. During the process, among many kinds of defects generated, a newly defined defect phenomenon so called backflow has appeared. It is a tendency of metal bulging in the radial direction on the wall as the roller passes through the deformation zone. In this paper, the mechanism of the backflow is studied as well as the process conditions to prevent backflow by establishing a numerical analysis procedure using SHAPE-RR FEM program. Result of FE analysis of the aluminum wheel flow forming is verified with flow line of experimental results. It was shown that bulging due to the backflow had been successfully simulated. It is concluded that the load of headstock is a major influence on the backflow.