By using finite element method, the causes of forming defects such as shortage of material and punching recess thickened during drill pipe joints forging were studied and some solutions were put forward. According to the numerical simulation results, one forming defect named shortage of material caused by the metal irregular flow at the bottom of necking die, which can be resolved by reducing the die forming-angle and increasing the width of the punch. On the condition with D0/d0≤2.6 (D0 refers to outer diameter, d0 refers to inner diameter), necking process can be completed with one-step backward extrusion. The thicker punching recess is formed by the accumulated metal which was scraped by the punch during necking extrusion. This kind of defect can not be eliminated, but can be minimized by improving friction conditions.