Recently, fluctuation of plasma has been discussed not only in field of nuclear fusion but also semiconductor etching. New evaluation method is proposed using stochastic model for prediction of plasma fluctuation based on collisional-radiative model. Electron impact excitation of atoms is considered as a Wiener process. Revised Wiener process is applied to analyze change of densities of excited-level populations in short time by Malliavin derivative. By using this method, the density
fluctuation is evaluated from the view point of contribution of electron collision