One of the characteristics of coherent wind lidar is using narrow linewidth laser source. In order to study the influence of different line width light sources on the detection performance of lidar, the spectrum characteristics of the time current in and out of the coherent length were analyzed theoretically. Experiments show that when the detection distance was outside the coherent length, the signal amplitude of 100 kHz light source was about 30% lower than that of 1 kHz and 10 kHz light source, and the noise amplitude of some frequency bands was larger than that of the other two light sources. Therefore, in the design of short-range wind lidar, hundreds of kHz light source could be considered, while in the medium and long-range lidar with detection distance of several kilometers or more, tens of kHz light source could be considered.