The invention relates to a 5G communication filter dielectric ceramic piece semi-finished product and a forming method thereof. The 5G communication filter dielectric ceramic piece semi-finished product comprises a main body, wherein the main body is provided with a cross-shaped through hole and a linear through hole, the cross-shaped through hole is located in the edge of the main body, a first blind hole is formed in the front face of the main body, a second blind hole is formed in the back face of the main body, the main body is provided with an extension part, the extension part is locatedon the side, which is close to the cross-shaped through hole, of the main body, and the extension part is of an arc-shaped structure. The forming method comprises the steps of designing a mold, manufacturing a feed, carrying out injection molding, degreasing with a solvent, carrying out thermal degreasing and sintering. The extension part is added to the thin wall of the main body, one-time injection molding can be achieved, the injection molding defect of the 5G communication filter dielectric ceramic piece is effectively overcome, the product quality is guaranteed, and the yield is increased. In addition, 5G communication filter dielectric ceramic piece semi-finished product is simple in machining process, and suitable for batch production.