Abstract: It is proposed to get the piercing plug sprayed with a plasma coating in a bid to enhance its surface properties, and thus prolong its service life, and cut down the operation costs as well. With employment of the ANSYS FEM calculation software, transient state analysis of the plasma-spraying process is conducted, which leads to identification of the internal temperature distributions of both the piercing plug and the coating. Based on the result, the stresses at the plug-coating interface and inside the coating are analyzed, and influential elements related to the residual stress discussed, including the plug preheating temperature, the coating thickness, and the coating material, etc, resulting in a proper spray-coating process, and theoretic basis for enhancing service span of the piercing plug.