Abstract: High precision measurement and determination of spaceborne InSAR baseline is a key technology in the acquirement of digital elevation information, optical camera and laser range finder were adopted for dual-antenna InSAR system. However, due to the effect of geometry error and instrument error, Kalman filter was designed based on the baseline measurement system and the modal analysis of antenna mast in order to meet the reqiurement of the high precision of interferometric baseline. Simulations conducted show that the vector of interferometric baseline could be precisely estimated by the Kalman filter.