The conflict may occur between the theory design result and the practical range in the conventional impedance transformer design.The mathematic model of the conceptual optimal design is provided.An improved mind evolutionary algorithm(MEA) is adopted to implement the optimization.An improved self-adaptive similartaxis strategy is introduced

the fitness function suitable to the microstrip circuit design is discussed

and the optimization steps of impedance transformer based on MEA are given.The optimization is performed using Matlab and the optimal parameters satisfying design requirement are obtained.Finally a comparison of optimization results among improved MEA

genetic algorithm and Chebyshev is carried out

which shows that the value of voltage standing wave ratio(VSWR) is kept low in transmission band

the size of impedance transformer is comparatively small.And it also verifies the feasibility and superiority of the mind evolutionary algorithm in solving nonlinear optimization problems with many variables.