In this study, the stiffness and the flexibility of welded metal bellows of mechanical seal is studied numerically by changing the number of bellows membrane and the loading condition. The relationship between the number of membrane and the displacement, the stress and the flexibility are analyzed. For further improved the axial displacement, overall stiffness and the flexibility of the welded metal bellows membrane, the finite element analysis are conducted. The numerical results show that the maximum stress keeps constant value with increasing the number of bellows membrane under the same loading condition. The relationship between number of bellows membrane and stiffness as will as the flexibility are obtained. It is shown, stiffness is decreased and flexibility is increased with increasing of the number of the bellows membrane.