An optical frequency modulated continuous wave coherent lidar technology for velocity measurement based on the Doppler effect is presented. The technology uses all-fiber structure. It has advantages of high efficiency, low power consumption, stable and reliable performance, with good ability to adapt to a mobile platform. Radar principles, structures, data processing algorithms and other related parts are discussed in detail. Flying helicopter hanging results are also given: the maximum measurement velocity is 150 m/s, the measuring range is over 3 km, and the maximum measurement error is 0.08 m/s.