According to the principle of differential image motion,the full-time measuring system of atmospheric coherence length based on EMCCD camera was developed for observing stars.By analyzing the spectral distribution of sky background and the spectral response characteristics of EMCCD,spectral filter with central wavelength of 700nm was selected to suppress the incidence of sky background light.The main noise of measuring system is introduced,and the calculated limiting star magnitude is 7.35 in daytime.Stargazing experiments for some different magnitude stars in the Ursa Minor are carried out in the field.The results show that the measurement system has a good detection capability for star with magnitude 3 in daytime.By continuous measurements of atmospheric coherence length in all-day time,atmospheric turbulence intensity change curve of the whole layer in Changchun was obtained.