The invention discloses an optimization method for calculating wave absorbing impedance of metal backing electromagnetic wave absorbing materials. The method comprises the following steps: A, acquiring the complex permeability and the complex dielectric constant of the wave absorbing materials, B, calculating a first level matching thickness, a third level matching thickness and a fifth level matching thickness of the wave absorbing materials under each electromagnetic wave frequency respectively according to a matching thickness formula, C, calculating corresponding input impedance of each electromagnetic wave frequency under the mentioned matching thickness according to an input impedance calculation formula, D, calculating absorption characteristics according to a reflection loss strength calculation formula and/or the calculation result of the step B or the calculation result of the step C, and further preparing the wave absorbing materials. According to the optimization method for calculating the wave absorbing impedance of the metal backing electromagnetic wave absorbing materials, a matching thickness model and a transmission line theory are combined and adopted, the optimization of the impedance matching of the electromagnetic wave absorbing materials is made to be more effective, the preparation of the wave absorbing materials can be completed fast and accurately, and the method is suitable for various electromagnetic wave absorbing composite materials. The optimization method for calculating the wave absorbing impedance of the metal backing electromagnetic wave absorbing materials can be widely applied to the technical field of wave absorbing materials.