The invention discloses a direct wind lidar based on the difference stimulated Brillouin gain effect. In the scheme, a continuous laser device is adopted as a light source, after being modulated through a phase or intensity modulator, carrier frequency light of the laser device is used as detection light, and light with frequency at the two sides is used as double-frequency pump light for generating stimulated Brillouin scattering in optical fiber. Atmosphere echo signals and the double-frequency pump light are transmitted oppositely in the optical fiber, the signals carrying Doppler shift generate energy change due to stimulated Brillouin scattering, energy change is detected by a detector, wind speed information of the atmosphere echo signals can be obtained, and a frequency discrimination device is formed by the system. As the frequency discrimination device is used, the laser outgoing frequency is fixed to the middle point of the spacing distance between an absorption peak and a gain peak on a frequency spectrum, and laser frequency does not need to be locked. The lidar system has the advantages of being stable, high in measurement accuracy, low in cost, simple and compact in structure and the like.