An equation for humidity determination by double–frequency phase method of radioacoustic sounding and numerical estimation of the effect of atmospheric turbulence on its performance are obtained. They are applicable at any ratio between relaxation and sounding frequencies. Relative deviation of humidity averaged over its turbulent fluctuations from such a value in nonturbulent atmosphere is obtained assuming weak fluctuations of speed of sound, phase differences of two frequencies and that their densities are distributed by Gaussian law. The phase difference fluctuations distribution variance is calculated for a limited Gaussian beam in a turbulent medium with Karman spectrum. For sufficiently large values of structure characteristics of temperature and wind velocity (under convective conditions at a moderate wind) the relative deviation of average humidity in this case does not exceed 2•10–3% at altitudes 50–200 m and the rms error, due to turbulence, in humidity measurements by the phase method does not exceed 0.6%.