Abstract: The appropriate mathematical model is chosen to reduce the effects on the accuracy by comparing the differences of the displacement distribution before and after applying the glasses. The experiment shows that the protective cover glass of camera has an influence on the measurement accuracy, and the biggest variation of the coordinate of the image point is approximately 5 micrometers and the distribution of the variation consists with the radial distortion. Finally, the influence could be replaced by a radial distortion model and the experiment shows that this method can effectively reduce the effects of the glass on the measurement accuracy.