A theoretical design model for continuous phase plates (CPP) used in inertial confinement fusion is built to improve the focus beam quality and reduce the difficulty of CPP′s fabrication.Moreover,the traditional G-S algorithm is modified through choosing continuous initial phase,phase unwrapping,phase filtering and controlling the frequency spectrum of focal spot.The operational characteristic and the focal spot′s performance caused by the CPP designed by traditional G-S algorithm and modified G-S algorithm are analyzed comparatively.The surface designed by the modified method is smoother than the traditional G-S algorithm,and the root mean square (RMS) and capacity usage ratio of the focal spot caused by modified G-S algorithm are 16.9% and 98.6% respectively,which are all better than the traditional method′s 62.8% and 98.0%.The 10-100 μm modulations of focal spot are suppressed very well.It shows that the CPP designed by the modified method meets the process restriction and physical specifications very well.