The orbit resource of the geostationary satellite is becoming scarce with the increase of the human's space activity.The technology of multi-satellite sharing one orbit area is used.In the collocation satellites observation,the safety among the satellites is one of the most important problems that need to be solved.Three-way ranging measurement is always used.But it needs a long period of observation in order to get an accurate orbit. The differential phase delay can be obtained with high accuracy in connected-element interferometry. This kind of observable can give strong constraints in the plane-of-sky.One connected-element system is constructed and the data processing method is shown.The key technology of the data processing and the instrument are also described.