In a method and apparatus for forming a three-dimensional image for an inspection pattern, a reference intensity function of an inspection X-ray is formed in accordance with a continuous scanning depth, and is differentiated with respect to the scanning depth. The differential reference intensity function is decomposed into a start function and a characteristic function. The differential reference intensity function is then repeatedly integrated while a temporary vertical profile function is substituted for the start function until the temporary intensity of a reference X-ray is within an allowable error range. The temporary vertical profile function satisfying the error range is selected as an optimal vertical profile function. A surface shape is combined to the optimal vertical profile function along a depth of the inspection pattern to thereby form the three-dimensional image for the inspection pattern.