Numerical phase-screen method is described for computer simulation of atmospheric turbulence with predetermined spatial spectrum in the case of transversal wind. The method is based on the spatial smoothing of the initial uncorrelated random field using a spatial filter obtained by the inverse Fourier transform of the original spectrum. The method allows one to simulate phase screens of virtually arbitrary length and is free of some restrictions of the spectral method. Examples of Kolmogorov spectrum field simulation are presented.