The traditional frequency-modulated signal generation using only elect ronics cannot achieve high resolution because of the narrow bandwidth.On the other hand,beca use of the significant atmospheric attenuation,a large number of radar heads must be insta lled in a millimeter radar system for surveying a large area.So a distributed radar syste m is needed to deliver a highly accurate signal from the central office in order to save cost.I n this paper,an approach of frequency-modulated continuous-wave (FM-CW) signal generation bas ed on gain-switching wavelength tunable semiconductor laser is proposed.It is easy t o be extended and is tunable for both the central frequency and the wavelength.Mu lti-radar head distribution system,capable of multi-channel switching,can be achieved with t his approach by using radio-over-fiber technology.In our experiment,a CW signal with frequency of 20GHz and a FM-CW signal with bandwidth of 500MHz and central fr equency of 10GHz can be achieved．The experimental results comfirm the feasibility of our approach for millimeter wave FW-CW signa l generation.