Feasibility of Space-based Tracking Telemetry and Command System (TT&C) based on single satellite was analyzed. A new orbit determination method based on constringent estimation was proposed according to the mode of single satellite observation. In the process of the orbit determination, the law matrix was availably transformed by the constringent estimation to restrain error of singularity cased by law matrix. It was proved that the precision of constringent estimation is higher than the traditional method under the given conditions. Then the error transmitting coefficient (ETC) of observation was proposed, on the basis of the special characteristics of the single satellite observation, and the algorithm of orbit determination was designed. Finally the new method of constringent estimation was proved to be able to improve the precision of orbit determination in the mode of single satellite observation.