Present paper deals with the measurement errors in Talbot wavefront sensor under Gaussian illumination conditions. The measurement possibilities of wavefront sensor based on the self-imaging phenomenon is investigated theoretically and based on the simulation results. A theoretical model based on Fresnel regime is used in order to determine the intensity distribution in the near field. The effect of Gaussian field is described in the terms of spatial spectrum of the grating image. On the basis of four different gratings was shown that Gaussian field affects on the spatial spectrum of the grating self-image if Gaussian waist is less than two grating periods and self-images of used gratings are almost the same. Four kinds of gratings are tested for their performance in the wavefront sensor. Simulation results show that binary gratings with square and circle unit cells show less value of measurement error in comparison with gratings that have cosine and Gaussian profiles.