Abstract: The inter-satellite baseline plays a vital role in the formation flight satellites missions.The appropriate spatial states were chosen to determine the inter-satellite baseline based on the precision requirements.A mathematical model was established to associate the spatial states and the inter-satellite baseline.An error analysis method was also presented.Simulations in certain scenarios were carried out.The index such as the precision influence factor was calculated to depict the propagation relations between the two kinds of parameters.The baseline length was only correlated with the relative spatial states of the formation flight satellites,while the baseline angles were also correlated with the absolute attitude of the master satellite.The errors were amplified during the propagation from the satellite spatial states to the inter-satellite baseline.