In this paper, the law of radial envelope forming (REF) of thin wall cylinder with vertical reinforcements is studied by finite element numerical simulation. First, a finite element model for REF of thin wall cylinder with vertical reinforcements is established by using Deform-3D software. Then, the evolution and distribution of strain and metal flow velocity during REF of thin wall cylinder with vertical reinforcements are analyzed, and the growth law of vertical reinforcement during this REF is analyzed in detail. The results show that radial compression strain, circumferential tensile strain and axial tensile strain occur in the web. Radial tensile strain, circumferential compressive strain and axial tensile strain occur in the vertical reinforcements. The metal flows mainly in radial direction and circumferential direction during REF of thin wall cylinder with vertical reinforcements. The vertical reinforcements show nonlinear growth, and the middle part of the vertical reinforcement is higher than both ends of the vertical reinforcement.