Abstract: A study of a Gaussian fitting method for estimating subaperture centroids of ShackHartmann wavefront sensor has been made. The method is based on the prior knowledge that the intensity distribution of subapertures spot can be considered approximately Gaussian in form. We present results for several different light intensities and distances of subapertures spot both with and without detectors noise. A more accurate estimation of the local slopes can be achieved at low light levels in this way than with the standard firstmoment estimator.