The atmospheric coherence length instrument was used to measure atmospheric coherence length for several months in mountainous area of South China. The results show that atmospheric coherence length of November is greater than that of October and December. The measurement results in night are more complex than those of daytime. The results in latter half of the night are greater than those of first half of the night. The frequency results show that central value of atmospheric coherence length in daytime is 8.5 cm and central value of atmospheric coherence length in night is 13.0 cm. The frequency results of distributing atmospheric coherence length in daytime is mainly center around 6 cm to 12 cm, and the same value in night is mainly center around 10 cm to 18 cm. The mean value of atmospheric coherence length in night is apparently larger than that of daytime. Even the thin layer in surface layer can have much influence on turbulence of the whole atmosphere especially by day.