A generalized equation of motion for KED analysis of general flexible mechanisms has been developed by utilizing newly isoparametric finite element theory in this paper. As a natural result，the mass matrix is a positive definite consistent and time-independent one，and the two time-dependent and nonsymmetric matrice，that is，the “gyroscopic damping”and “centrifugal stiffness”ones，don't exist in the equation. Thus the equation with concise form may be derived and solved easily. Also based on the one-dimensional isoparametric beam elements，the equation for some flexible planar linkages has been derived in detail，and a numerical result of a planar for-bar linkage is presented in the paper.