For non-Kolmogorov turbulence, the anisoplanatiam error, the angular correlation function of Zernike polynomials, the residual phase structure function and the long-exposure OTF after low-order modes correction are analyzed. The modal correction coefficient is used to evaluate the influence of anisoplanatism error for compensation effectiveness of adaptive optical system used as low-order modes correction. The numerical computational results of t he modal correction coefficient and the long-exposure OTF for light beam horizo ntal atmospheric propagation are presented.