A method of displaying a 3D image is provided, which mainly proposes a real-time detection method of a viewing position, an optimum alignment method of a viewing position and a view, a dynamic multi-view 3D image combination method, and a design method of a static parallax barrier device, to eliminate defects of auto-stereoscopic display especially in the case that a common flat-panel display screen and a static parallax barrier device are used to display a 3D image, so as to effectively solve problems of a ghost image, a pseudo stereoscopic image, and insufficient viewing freedom in horizontal and vertical directions on an optimum viewable plane, thereby achieving the objectives of greatly improving the 3D image quality and the convenience of use.