In this work,based on the construction and basic working principle of multi-beam wind measuring system,the optical correlation properties of back-scattering signals measured by two detectors were theoretically analyzed combining with the small distribution theory.Meanwhile,four kinds of optical correlation methods were proposed to calculate the wind speed,ie.,embracing peak-delay method,slope method,frequency method,and Briggs method.According to the real-place verifying experiment,the results show that the peak-delay method,slope method and frequency method have high measurement precision with errors less than 5%.