Abstract: The Rytov approximation theory is applied to the angle-of-arrival fluctuation and the analytical expressions are developed for variance and power spectrum associated with the angle-of-arrival fluctuation of unbounded plane waves and spherical waves in strong turbulence regime. The derived expressions are then compared with the previous weak fluctuation theory, and effects of the scattering disk scale on power spectrum are analyzed. Results show that the derived displacement variances extending into weak turbulence regime are in good agreement with those of the traditional weak-fluctuation theory and are valid in all turbulence regimes; The angle-of-arrival fluctuation tends to saturate with increasing Rytov variance; The high-frequency power spectra drops at a much faster rate along with t