The Fried′s Coherence Length quantitatively was measured by means of two different methods in the convective turbulent tank for adaptive compensation experiments. The spectra of arrival angle fluctuations and its probability distribution were given. It was showed that the spectra of arrival angle fluctuations agreed with the theoretical prediction “-8/3” power law. The fluctuations of phase fellowed a normal distribution. The χ 2 distribution appeared to be a reasonable assumption for variance of arrival-angle fluctuations. The spectrum of arrival-angle in X axis same as the spectrum in Y axis indicated obviously that the turbulence in the tank was isotropic feature. The experimental results between the Fried's Coherence Length and temperature differences between heated-plate and cooled-plate, agreed with the similar relationship in fluid mechanics and thermodynamics experiments in the convective tank.