The importance of millimeter wave frequency synthesizers was introduced briefly, the advantage and disadvantage of two schemes of millimeter wave frequency synthesizers were analyzed, and a design scheme of millimeter wave frequency synthesizers was put forward by the combination of their merits and the Direct Digital Synthesis(DDS) technology. A systematic experiment of the scheme was operated, and the results showed that the phase noise was -85dBc/Hz@10kHz. so the performances of the whole millimeter wave communication system were improved.