The invention relates to a metal artifact correcting method of a cone-beam CT (computed tomography) system. The metal artifact correcting method of the cone-beam CT system comprises the steps of separating a metal projection image M (x, y) from an original orthographic projection image f(x, y), reconstructing the metal projection image M (x, y) to obtain a CT reconstruction image XMetal of the metal part, reducing the metal projection image M (x, y) of the original orthographic projection image f(x, y) to obtain a projection image fres(x, y) without the metal part, reconstructing the projection image fres(x, y) without the metal part to obtain a CT (computed tomography) image Xres without the metal part, and adding a CT (computed tomography) image Xmetal of the metal part with the CT (computed tomography) image Xres without the metal part to obtain a final CT (computed tomography) reconstruction image Xcorrection after the correction of a metal artifact. Coordinates are not changed in the metal artifact correcting method, so that the image space resolution is not lost, and the image quality is enhanced.