Abstract: Direct digital synthesizer (DDS) is the latest technique for frequency synthesis, which has the advantage of fine frequency resolution and fast switching speed, but it has a high level of spurious frequencies. This paper mainly presents several methods in reducing the parasitic sidelobe level in phased arrays, and uses a method for randomizing the phase errors to improve DDS on the condition of a phase truncation. This method can reduce the level of spurious frequencies, and is a good attempt on the application of DDS.