As to using the method of three dimensional finite element,this study has analyzed the stress distribution of the porcelain fused to metal crowns with three different labial margin configurations under the forces from diverse direction.The results showed that the chamber margins exhibited fewer tensile stresses than the shoulder or shoulder with a bevel margins.The labial margin exhibited more tensil stresses when the incisal edge of the crown was loaded with labial forces.so,we provide the mechanical basis for the conclusions as follows: (1)The labial chamber margin is preferable to shoulder or shoulder with a bevel margin. (2)The porcelain may fracture when the incisal edge of porcelain fused to metal crown is loaded with labial forces.