Abstract: The baseline between the formative flying satellites can be obtained by the relative positioning based on spaceborne GPS receivers.However,it is not identical with the one applied in the spaceborne InSAR height measurement.The associated modeling from the GPS measurement baseline to the InSAR height acquisition baseline is presented.Several steps are included in the overall conversion,such as the offset modification between the phase center and the geometric center of antennas,the fixing position modification from the GPS receiver to the SAR antenna and the reference frames conversion of the baseline vectors.The modification and conversion formulas are deduced,and the corresponding precision analyses are also carried out.Simulations show that the baseline vector offset caused by the antenna phase center variation in a loose formation within the critical baseline range must be modified,for it is at the sub-millimeter level and sometimes even higher and reaches the precision level of the InSAR baseline requirement at the centimeter level.The baseline modification error introduced by the reference frames conversion error is at the sub-millimeter level as the relative attitudes are usually small between three-axis stabilized satellites in a formation.