A FEM computing technique for hydraulic hoist cylinder of lock miter gate is introduced. Through setting up the two dimensional beam element model suitable for this kind of cylinder and adopting the beam element rigidity matrix derived from the beam - pillar theory and potential energy stationary value condition, a finite balance equation and a stability characteristic equation are established. In combination with the border conditions, the joint displacement, element internal stress and critical pressure of a cylinder may be calculated. A set of cylinders for an illustration are calculated using this FEM method. At last, the features of this algorithm and its application range are discussed. 