Contrast to the measurement results of thermometer device, the accuracy of the measurement results by atmospheric coherence length monitor was certified. The deviations of the measurement results and the reasons for them were analyzed. Horizontal atmospheric coherence length at Bohe sea level and seaside and in Hefei had been measured by atmospheric coherence length monitor. The results show that horizontal atmospheric coherence length at sea is greater than that at seaside and it is the smallest in Hefei. Horizontal atmospheric coherence length in Hefei has typical diurnal variation and changes about 4?10 cm at morning transition moment and 4?15 cm at evening transition moment. Horizontal atmospheric coherence length at seaside changes about 8?15 cm and its feature is the same as Hefei and it keeps about 12 cm after evening transition moment. Horizontal atmospheric coherence length at sea changes about 9?12 cm at morning transition moment while it increases rapidly from 15 cm to 50 cm and then decreases sharply to 28 cm after about 2 h at evening transition moment. Taking the characteristics of different underlying surface, weather condition and the influence of the conversion between sea wind and land wind into consideration, the reasons of these experimental results are given.