A method for an ion implantation is provided. First, a non-parallel ion beam is provided. Thereafter, a relative motion between a workpiece and the non-parallel ion beam, so as to enable each region of the workpiece to be implanted by different portions of the non-parallel ion beam successively. Particularly, when at least one three-dimensional structure is located on the upper surface of the workpiece, both the top surface and the side surface of the three-dimensional structure may be implanted properly by the non-parallel ion beam when the workpiece is moved across the non-parallel ion beam one and only one times. Herein, the non-parallel ion beam can be a divergent ion beam or a convergent ion beam (both may be viewed as the integrated divergent beam), also can be generated directly from an ion source or is modified from a parallel ion beam, a divergent ion beam or a convergent ion beam.