High pressure torsion (HPT) is one of the most promising severe plastic deformation (SPD) techniques to produce ultrafine-grained (UFG) or nano-grained (NG) materials via introducing very large plastic strain. This study aims to understand the texture evolution mechanism during HPT by examining the nickel single crystal. The predicted textures after different HPT rotation angles based on a three-dimensional crystal plasticity finite element method (CPFEM) model agree well with the experimental measurements. Both the modelling and experiment show that the crystallographic orientation rotates gradually towards different ideal torsion texture components during HPT deformation, and three steady-state stages and two transition stages can be divided according to the texture evolution history. The crystal rotation during HPT process has been partitioned into three components around the radial direction, tangential direction, and axial direction, respectively. The texture evolution history and mechanism have been examined and discussed in details.