According to the characteristic of dielectric constants of the noble metals in the visible and near-infrared region,a first-order perturbation theory is applied to obtain the propagation constants of the TE and TM modes in the symmetrical metal-cladding optical waveguide. In the light of the great propagation loss of symmetrical metal-cladding optical waveguide,a method that sub-millimeter scaled guiding layer is used to depress the propagation loss is proposed. Calculated results of first-order perturbation agree well with the numerical approach.