To measure DUT’s resistance, capacitance, inductance, quality factor and so on, the core is to carry out impedance measurement. At present, there are many impedance measurement methods to choose, such as bridge method, resonant method, IV method, RF IV method, network analysis method, autobalancing bridge method, etc. Each of the methods has advantages and disadvantages. In the design of impedance measurement using autobalancing bridge method, the signal generating function of the signal source circuit and the modulation demodulation circuit are respectively adopted by two DDS. In order to achieve the balance of the autobalancing bridge quickly and accurately, according to different measurement frequency, demand phase synchronization of two DDS output signals. In this paper, deal with three aspects of the reference clock signal, the update clock signal and the reference clock multiplier, have simple design, easy to achieve. Widely used in many fields such as LCR meter, capacitance meter, impedance analyzer, function generator, etc.