Abstract: As the highest measurement precision attitude sensor, attitude determination is the most basic and critical section in navigation. To analyze the impact of star distribution on least square attitude measuring precision, the definition of the attitude angle was described, the problem-solving process by least square method was researched, and the condition number of the coefficient matrix, that leads to poor precision under a certain observational error, was derived from the view of mathematical. Lastly, three sets of typical star distribution under different conditions were simulated, calculate the results and conduct the statistics, the simulation results indicate that measurement precision is influenced by different locations of the star group in image and different device parameter models for star sensor, besides the relative position of the star group described by condition number.