For analyzing and avoiding the influences resulting from zero position error of control algorithm for controlling the exposure dose invariably on the Concave Spherical Substrate(CSS) via photolithography technology,the mathematical models and relation curves of zero position error versus scanning linear velocity and arc length are deduced and given respectively.After analyzing the relation curves,the influences resulting from zero position error are obtained as follows:vertical zero position error causes that line width of parts of lines are wider or narrower than ideal value and line width change monotonically,and the level zero position error causes that actual scanning arc length is longer or shorter than required value,which results in parts of edge of the CSS lacking of lines even grids.The opto-electronic encoders are adopted as feedback sensor of vertical and level axes,and the velocity and position dual closed-loop control method is taken,which realizes the zero positioning precisely and guarantees the exposure dose invariably,as well as scanning arc length accurately.Several eligible concave spherical meshes have been fabricated