Abstract:  Transformation optics is a newly proposed theory which involves into a powerful tool set for the design of various novel electromagnetic devices that are difficult to conceive using regular methods. By taking advantage of the invariance of Maxwell Equations upon coordinate transformation, transformation optics yields a precise prescription of spatially-varying and anisotropic optical constant to guide wave propagation at our wills. It is well known that traditional waveguide bends inherently suffer from reflections and mode distortions since a wave has to travel along paths of various lengths counting on the radial or cornered location inside the bends. To eliminate such vast reduction of transmission, we utilize the method of transformation optics to design a metamaterial placed in a 90 degree waveguide bend which can completely suppress the reflections and modes perturbations to support perfect transmission. The constitutive parameters of the associated metamaterial in the waveguide bend are analytically obtained, and are validated available using numerical simulations based on the finite element method. We further propose a stacked bilayer structure to substitute unprocurable anisotropic material inside the waveguide bend on the basis of Effective Medium Theory. The bilayer structure are composed of both isotropic materials which are more prone to prepare in laboratory fabrication. The numerical simulated results completely validate the correctness of our theoretical analysis and feasibility of practical application.