Abstract: The distribution of guide stars in the field of view (FOV), especially in case of considering the magnitude error, gives an important influence to the design of optical system of star tracker, the selection of guide stars and the star field recognition algorithm itself. In this paper, the distribution of guide stars in ideal cases is described and based on the threshold of magnitude and measured uncertainty, the prediction of distribution in case of considering the magnitude error is derived. A Monte Carlo experiment demonstrates that the statistical result is well coincided with the prediction by using above mentioned method.