A new continuum method based on the concept of energy equivalence is introduced to represent a large platelike periodic lattice structure as an equivalent continuum plate. The procedure for developing an equivalent continuum plate involves the use of existing well-defined finite-element matrices for easy calculation of strain and kinetic energies contained in a representative lattice cell of the lattice plate. The strain and kinetic energies contained in the representative lattice cell of lattice plate and the finite-element of equivalent continuum plate are expressed in terms of continuum degrees-of freedom introduced in this paper with corresponding reduced stiffness and mass matrices. The structural properties of the equivalent continuum plate are then obtained by simply equating the reduced stiffness and mass matrices for the equivalent continuum plate to those for the lattice plate. Free vibration analyses for the continuum plates are conducted to evaluate the continuum method proposed in this paper. Numerical tests show that the present continuum method gives very reliable structural and dynamic properties compared with other well-recognized continuum methods.