A method of discriminating Doppler shift using Fizeau interferometer and linear PMT array for a direct-detection wind Doppler lidar is proposed. At first, its working principle is introduced. According to the spectral character of Fizeau interferometer, optimum design of frequency shift discrimination interferometer is presented, and the designed Fizeau interferometer has the cavity length of 150 mm and reflectivity of 0.755 from plate. The numerical simulation for wind speed measurement using the Fizeau interferometer and PMT array detector is also presented. The effect of molecular backscattering taken as background noise is analyzed. The error of wind speed measurement using system with Fizeau interferometer and linear PMT array is calculated. The results show that wind velocity error can be less than 0.56 m/s in the 5 km range under 30 s average time using the proposed system.