Abstract: The two-way Doppler equation isderivated according to the concept of the two-way Doppler range-rate measurement. The major measure methods and error sources are suggested and the analysis of the average error of the Doppler measure method is put forward. For direct sensing, the Doppler factor is derivated using the geometry method. A more ideal measure method based on discussing two conventional measure methods is suggested.The method has been applied to a practical equiqment. In order to analyse the range-rate error, ten major error sources is taken into acc0unt. Among other things,the tenth error source must be considered in the case of the rotation satellite using paetical antennas. Finally, the emphasis is laied on the average error of the Doppler measure method. On the basis of getting a clear understanding of the average error concept, the major factors to influene the error are analysed.