Abstract: A novel phased array passive microwave imaging system based on direct digital synthesizer (DDS) technology is proposed and implemented, which uses DDS to indicate the local oscillator signal for the RF channel after its up-conversion with a fixed-frequency local oscillator. DDS is used as the equivalent phase shifter for the phased array imaging system due to its high phase resolution and fast phase shifting capability. Compared to the traditional phased array imaging schemes which use the digital phase shifters, the proposed imaging scheme has the capability to make almost continuous high density scanning for the field of view with the advantages of high scanning speed, high resolution of phase shifting and high scanning pixels. The measured imaging results show that the imaging schemes based on DDS have the advantages of better imaging quality, high imaging speed and lower cost, which demonstrates that it is a promising technology for microwave and millimeter wave imaging.