Using active lap to polish an aspherical mirror is a dynamic proceeding, so the translation and spin of spindle, the spin, tilt, deformation, and rise and fall of the lap; and the spin of the primary mirror all together must be kept in step, under the computer control. According to author's ??910 mm, F/2, parabolic primary mirror and our active lap parameters, the author analyzes the deformation character of active lap base, that is, its deforming quantity, deforming velocity and deforming acceleration, and the difference between precision deformation and approximative analysis; the distance of rising and falling on 3-hoist points of the stressed lap back, that is, its moving velocity and acceleration; the relationship between reality deforming quantity of stressed lap and the measuring quantity using LVDT on measuring shelf. Also the relationship and features about deformation and hoisting movement with V1 (lap moving velocity along the crossbeam) and V2 (lap spinning speed around its spindle) are analyzed. Based those analyses, the author can guide to design mechanics and electronics of active lap, and guarantee all these movement keep in step.