On the basis of the assumption of Preston, the removal function of grinding head with petal-like section, in the form of dual-rotor movement, in the polishing process of optical elements, is studied and derived. A method, using a finite number of discrete points and its arc length to express the grinding head of petal-like section is proposed. And the scope of application of this method is figured out. On the basis of this method, the expression of the removal function of grinding head with petal-like section, in the form of dual-rotor movement, is derived. According to the curve approximation principle of adjustable steps, the approximation algorithm of Gaussian-like removal function, which is the target function, is studied. And the parameters of dual-rotor polishing modal with cosine-like removal function are got. It is proved that gaussian-like removal function can be got from polishing technology of dual-rotor movement.