The invention discloses a sectional bending mould for machining heavy forging, includes a inclined concave mould, and a convex mould and a back pressure mould matching with the concave groove, wherein, upper surface of the inclined concave mould has a concave groove cavity with both sides end face of inner-low and outer-high inclined surface, lower surface of the convex mould has a concave plate matching with the concave groove cavity, appearance of lower surface of the convex plate is matching with shape of inner surface of middle of the forging, the back pressure mould is disposed inside the concave groove cavity with its contour of upper surface matching with shape of non-bending area of outer side of middle of the forging, the lower surface is provided with a elastic mechanism to connect with bottom of the concave groove cavity, the elastic mechanism can push the back pressure mould to upper surface of the inclined concave mould without external force. The invention can be used for machining bending of heavy forging, and has advantages of low cost and good quality.