In view of the commonly used downlink signal of deep space explorer and the characteristics of radio interferometry,a novel interferometry method is proposed to process DOR signal and data-transmission signal simultaneously for frequency synchronization. Firstly, the difference phase of the two kinds of signal is obtained by correlation. While, the time delay is estimated by utilizing DOR signal's difference phase and is modeled during the processing. Then the phase difference between DOR and data-transmission signal at data signal carrier is acquired by using the constructed time delay model, compensating the difference phase of data-transmission signal. Finally,the difference phase of DOR signal and the compensated difference phase are processed for frequency synchronization and time delay estimation. The processing results of measured data in China deep space TT&C network show that the time delay accuracy is improved significantly by fusion process, while the improvement is decreased lightly with the influence of medium delay error. The proposed method improves the accuracy of time delay estimation just by fusion process, which not only promotes the signal use efficiency, but also enhances the robust of the TT&C system,having special significance in emergency situation.