Through mathematical analysis and calculation, the author considers that the former mechanical structure(used to axialsymmetrical asphere) must be modified when being used to off-axis segment. This point is different from Dr. H.M.Martin[3]. The author puts forward two mechanical structures, electrical control types, and draws up feature graphs of movement, deformation and hoist etc. then to analyze the moving and deforming features of stressed lap on off-axis segment. At last the author gives new imagination for look-up tables and how to read out data.