In order to investigate the optimal workpiece geometry of pure Ti extruded by equal channel angular pressing (ECAP) at room temperature, deformation behaviors of Ti billets were studied by means of three-dimensional (3D) finite element simulation. The optimal dimensions of pure Ti billets have been obtained by analyzing the influences of workpiece shapes and sizes on damage factor, pressing force, and strain rate distribution at the shearing band. The analytical results show that the square billet exhibits a much larger damage factor than the round billet, and also than the critical damage value of pure Ti materials, which suggests that the square billet is hard to make deformation and prone to trigger surface cracks. The 3D model reveals that the round billet with a diameter of 15 mm is optimal due to the smallest damage factor, proper pressing load and relatively homogeneous strain distribution. Under the optimal workpiece geometry according to numerical simulation results, ECAP experiment of the pure Ti round billet with a diameter of 15 mm can be successfully processed at room temperature. Additionally, hardness distribution of the as-ECAPed Ti rod is homogeneous at cross-section, which is consistent with the prediction of uniform strain distribution by 3D simulation.