Wind lidar based on Fizeau interferometer detects displacement of fringes of the Fizeau due to Doppler shift by a linear detector. The measurement precision may be influenced by the system noise, the linewidth of the laser, the divergence angle of the beam, the spatial variations in intensity of the incident and scattering light before they come to the interferometer and the inner structure of the detector. These factors are analyzed to provide suggestion on how to improve the measure precision.