To study the real-time estimation method on tether parameters for orbital motion of tethered satellite system,after analyzing the main problems in current estimation methods,the measurement information of a three-axis tether tensiometer and the extended Kalman filter were introduced,then a real-time estimation method was developed for large-angle change on tether swaying angle.This estimation method was deduced and demonstrated in detail.Finally,the validity of the estimation method was verified by simulation results and a preferable estimation precision was obtained.