A method of combining independent frequency sources of the same frequency and phase is proposed to improve the phase noise of the frequency source. Due to the inconsistency of the hardware, however, there is a certain phase difference between independent sources, so the phase noise of the combined frequency source is not close to the theoretical value and is even degraded. This paper proves that combining multiple frequency sources the frequency and phase of which are equal or approximate can improve the phase noise performance of the frequency source, and carries out the theoretical simulation with MATLAB. Aimed at the problem of phase non-synchronization or phase difference between two frequency sources, an adaptive tracking algorithm was proposed to realize the phase synchronization between two different frequency sources. Finally, this paper provided the theoretical simulation results of the proposed algorithm. From the theoretical proof and simulation results, relative to the initial frequency source, the phase noise of the combined frequency source signal is improved by 3 dB. In this paper, an adaptive tracking algorithm was also proposed. The algorithm can control the phase difference between the two initial frequency sources to be less than 10°, the expected effect of which has been achieved.