With the use of the method of extended boundary conditions and Haar wavelets, the problem of diffraction of a cylindrical or plane wave by concave and concave-convex screens is numerically solved. The influence of the position of a cylindrical wave source (the direction of a plane wave propagation) and the influence of the screen curvature on the field structure near the screen surface is investigated. The results of computation are interpreted on the basis of the geometric optics method and the geometric theory of diffrac tion.