Abstract: Direct digital synthesizer (DDS) is a kind of ne w frequency synthesizer technique. With it signal parameter can be switched int o signal wave. In the field of traditional linear FM-CW ranging, voltage contro lled oscillator(VCO) is modulated by triangle wave and outputs linear FM-CW sig nal, but the sweep nonlinearity and low frequency resolution of voltage controll ed oscillator(VCO) make great influence to the range precision of linear FM-CW radar. In this paper, the direct digital synthesizer(DDS) is used in linear FM- CW radar instead of voltage controlled oscillator, the problem is solved well. F FT algorithm is realized by DSP, and the system is controlled by singlechip and the terminal uses liquid crystal display(LCD).