The invention discloses a base body used for an X-ray conversion target and a machining method thereof. The base body comprises a substrate and a frame, wherein an accommodating groove is formed in the frame, and the substrate is arranged in the accommodating groove and integrated with the frame. The machining method comprises the step of S1 carving a blank flat entirely into the base body. The base body used for the X-ray conversion target is easy to machine, good in sealing performance and high in mechanical strength, dimensional accuracy of machining and heat dissipating capacity in use are guaranteed, and severe thermal deformation does not occur easily.