X-rays can be reflected off smooth metallic surfaces at very shallow angles grazing incidence. Such reflections are particularly efficient for metals with high density, such as gold, platinum or iridium. The reflection, similar to those radiations in the optical wavelengths, is non-dispersive.

For detail http://asd.gsfc.nasa.gov/xrays/MirrorLab/xoptics.html

Dear Tabrej Shaikh: The link does not answer my question. The link is about some specially designed mirrors which had been used for focusing of x-ray. But my doubt is why simple mirror or lens that can be used for focusing of light not applicable for x-ray.

Visible light lenses cannot be used for x-rays because (1) the index of refraction is very very close to 1, and therefore the focal length becomes impractically long and (2) the absorption for x-rays is much too high. You can design refractive lenses for x-ray using low-Z materials with low absorption (e.g. Beryllium), very small radii of curvature and then stacking many identical lenses.

Mirrors for visible light work for almost any angle of incidence. X-rays are reflected only for very shallow angles (as already pointed out by Tabrez). Therefore mirror geometries designed for visible cannot work for x-rays. But again, as Tabrez pointed out in his link you can design mirrors for use with x-rays and they can be used for focusing.

The third way of focusing x-rays is with Fresnel zone plates.

http://www.x-ray-optics.de/

I've never heard of x-ray "focusing". Interesting concept which I will research further. Beam "hardening" with Al "filters" is all I know about from a medical imaging standpoint. That's not really focusing- just raising the average energy of the filtered beam to reduce dose to skin and superficial soft tissue.