The principle and instrument for the measurement of atmospheric coherence are described and the results measured at Changsha are reported in this article. The impact of the atmospheric coherence length on the probability of "lucky image" is analyzed. The experimental data is coincide with the near-earth line turbulence strength, changes in atmospheric coherence length significantly affect the probability of "lucky image" , it is verified that the measurement method can provide certain reference significance of the parameter selection of lucky imaging.