The present invention provides a method for designing the parameter of a wave trap of the magnetic suspension flat high-speed rotor system. The magnetic suspension flat high-speed rotor system is considered with a kinetics model of a first order elastic mode and is translated into a complex-coefficient single-variate open-loop transfer function. The double-frequency Bode chart of the single-variate open-loop transfer function of the complex coefficient in different rotary speed is drawn. The phase angle allowance of the first order elastic mode in each rotary speed is calculated, and the series-connected progression, central frequency and polar point amortization of the elastic self-excited vibration restraining used wave trap are designed according to the phase angle allowance curve. Basing on the double-frequency Bode chart the invention presents a method for designing the parameter of the wave trap which comprises a magnetic suspension flat high-speed rotor system with strong gyroscopic effect and is used for restraining the first order elastic self-excited vibration. Compared with the common multiple-variate system designing method such as state space method and the like, not only has excellent immediacy and robustness, but also can minimize the effect of the wave trap to the nutation stability, and thus the invention the invention is more suitable to be used in the actual magnetic suspension high-speed rotor system such as the magnetic suspension fly wheel, and the magnetic suspension control moment gyroscope and the like.